The linter in bug 1566315 has already detected over 200 prefs in all.js that could be duplicates:

dom.quotaManager.testing
dom.inputevent.datatransfer.enabled
dom.script_loader.binast_encoding.enabled
browser.display.document_color_use
browser.display.use_system_colors
browser.display.foreground_color
browser.display.background_color
browser.anchor_color
browser.active_color
browser.visited_color
browser.underline_anchors
browser.display.use_focus_colors
browser.display.focus_background_color
browser.display.focus_text_color
browser.display.focus_ring_width
browser.display.focus_ring_on_anything
browser.display.focus_ring_style
media.opus.enabled
media.wave.enabled
media.webm.enabled
media.navigator.mediadatadecoder_vpx_enabled
media.navigator.mediadatadecoder_h264_enabled
media.benchmark.vp9.threshold
media.benchmark.frames
media.benchmark.timeout
media.media-capabilities.enabled
media.media-capabilities.screen.enabled
media.encoder.webm.enabled
media.autoplay.enabled.user-gestures-needed
media.av1.enabled
media.av1.use-dav1d
layers.geometry.opengl.enabled
layers.geometry.basic.enabled
layers.geometry.d3d11.enabled
apz.allow_double_tap_zooming
apz.allow_immediate_handoff
apz.allow_zooming
apz.android.chrome_fling_physics.enabled
apz.android.chrome_fling_physics.friction
apz.android.chrome_fling_physics.inflexion
apz.android.chrome_fling_physics.stop_threshold
apz.autoscroll.enabled
apz.axis_lock.mode
apz.axis_lock.lock_angle
apz.axis_lock.breakout_threshold
apz.axis_lock.breakout_angle
apz.axis_lock.direct_pan_angle
apz.content_response_timeout
apz.drag.enabled
apz.drag.initial.enabled
apz.drag.touch.enabled
apz.danger_zone_x
apz.danger_zone_y
apz.disable_for_scroll_linked_effects
apz.displayport_expiry_ms
apz.enlarge_displayport_when_clipped
apz.fixed-margin-override.enabled
apz.fixed-margin-override.bottom
apz.fixed-margin-override.top
apz.fling_accel_base_mult
apz.fling_accel_interval_ms
apz.fling_accel_min_velocity
apz.fling_accel_supplemental_mult
apz.fling_curve_threshold_inches_per_ms
apz.fling_friction
apz.fling_min_velocity_threshold
apz.fling_stop_on_tap_threshold
apz.fling_stopped_threshold
apz.frame_delay.enabled
apz.keyboard.passive-listeners
apz.max_tap_time
apz.max_velocity_inches_per_ms
apz.min_skate_speed
apz.minimap.enabled
apz.one_touch_pinch.enabled
apz.overscroll.enabled
apz.overscroll.min_pan_distance_ratio
apz.overscroll.stop_distance_threshold
apz.paint_skipping.enabled
apz.peek_messages.enabled
apz.pinch_lock.mode
apz.pinch_lock.span_breakout_threshold
apz.pinch_lock.span_lock_threshold
apz.popups.enabled
apz.relative-update.enabled
apz.printtree
apz.record_checkerboarding
apz.second_tap_tolerance
apz.test.logging_enabled
apz.touch_start_tolerance
apz.touch_move_tolerance
apz.velocity_bias
apz.velocity_relevance_time_ms
apz.x_skate_highmem_adjust
apz.y_skate_highmem_adjust
apz.x_skate_size_multiplier
apz.y_skate_size_multiplier
apz.x_stationary_size_multiplier
apz.y_stationary_size_multiplier
apz.zoom_animation_duration_ms
apz.scale_repaint_delay_ms
layout.scroll.root-frame-containers
layout.scrollbars.always-layerize-track
gfx.layerscope.enabled
gfx.layerscope.port
gfx.perf-warnings.enabled
gfx.color_management.mode
gfx.color_management.rendering_intent
gfx.color_management.enablev4
gfx.downloadable_fonts.otl_validation
gfx.downloadable_fonts.keep_color_bitmaps
gfx.downloadable_fonts.validate_variation_tables
gfx.font_rendering.coretext.enabled
gfx.font_rendering.ahem_antialias_none
gfx.canvas.remote
gfx.draw-color-bars
gfx.logging.painted-pixel-count.enabled
gfx.ycbcr.accurate-conversion
gfx.compositor.glcontext.opaque
gfx.webrender.highlight-painted-layers
gfx.webrender.blob-images
gfx.webrender.blob.paint-flashing
gfx.webrender.dl.dump-parent
gfx.webrender.dl.dump-content
gfx.webrender.picture-caching
gfx.webrender.start-debug-server
accessibility.browsewithcaret
toolkit.scrollbox.verticalScrollDistance
toolkit.scrollbox.horizontalScrollDistance
browser.dom.window.dump.enabled
devtools.console.stdout.chrome
devtools.console.stdout.content
nglayout.debug.widget_update_flashing
print.font-variations-as-paths
privacy.trackingprotection.origin_telemetry.enabled
javascript.options.streams
security.fileuri.strict_origin_policy
clipboard.autocopy
mousewheel.transaction.timeout
mousewheel.transaction.ignoremovedelay
mousewheel.acceleration.start
mousewheel.acceleration.factor
mousewheel.system_scroll_override_on_root_content.vertical.factor
mousewheel.system_scroll_override_on_root_content.horizontal.factor
general.smoothScroll.mouseWheel.durationMinMS
general.smoothScroll.mouseWheel.durationMaxMS
general.smoothScroll.pixels.durationMinMS
general.smoothScroll.pixels.durationMaxMS
general.smoothScroll.lines.durationMinMS
general.smoothScroll.lines.durationMaxMS
general.smoothScroll.pages.durationMinMS
general.smoothScroll.pages.durationMaxMS
general.smoothScroll.other.durationMinMS
general.smoothScroll.other.durationMaxMS
general.smoothScroll.mouseWheel
general.smoothScroll.pages
general.smoothScroll.durationToIntervalRatio
general.smoothScroll.currentVelocityWeighting
general.smoothScroll.stopDecelerationWeighting
general.smoothScroll.msdPhysics.enabled
general.smoothScroll.msdPhysics.continuousMotionMaxDeltaMS
general.smoothScroll.msdPhysics.motionBeginSpringConstant
general.smoothScroll.msdPhysics.slowdownMinDeltaMS
general.smoothScroll.msdPhysics.slowdownMinDeltaRatio
general.smoothScroll.msdPhysics.slowdownSpringConstant
general.smoothScroll.msdPhysics.regularSpringConstant
layout.css.report_errors
layout.css.scroll-snap.proximity-threshold
layout.css.scroll-snap.prediction-max-velocity
layout.css.scroll-snap.prediction-sensitivity
layout.css.scroll-behavior.enabled
layout.css.scroll-behavior.spring-constant
layout.css.scroll-behavior.damping-ratio
layout.frame_rate
layout.display-list.dump
layout.display-list.dump-content
layout.display-list.dump-parent
layout.display-list.retain
layout.display-list.retain.chrome
layout.display-list.rebuild-frame-limit
layout.animation.prerender.partial
layout.animation.prerender.viewport-ratio-limit-x
layout.animation.prerender.viewport-ratio-limit-y
layout.animation.prerender.absolute-limit-x
layout.animation.prerender.absolute-limit-y
dom.ipc.plugins.asyncdrawing.enabled
fission.autostart
mousewheel.system_scroll_override_on_root_content.enabled
image.animated.decode-on-demand.threshold-kb
image.animated.decode-on-demand.batch-size
image.animated.resume-from-last-displayed
image.cache.factor2.threshold-surfaces
image.cache.max-rasterized-svg-threshold-kb
image.decode-immediately.enabled
image.downscale-during-decode.enabled
image.infer-src-animation.threshold-ms
image.layout_network_priority
image.mem.discardable
image.mem.animated.use_heap
image.mem.debug-reporting
image.mem.shared
image.mem.volatile.min_threshold_kb
image.webp.enabled
gl.require-hardware
gl.multithreaded
gl.ignore-dx-interop2-blacklist
gl.use-tls-is-current
gl.allow-high-power
webgl.1.allow-core-profiles
webgl.force-enabled
webgl.disabled
webgl.disable-angle
webgl.disable-wgl
webgl.min_capability_mode
webgl.disable-extensions
webgl.msaa-force
webgl.prefer-16bpp
webgl.default-low-power
webgl.default-no-alpha
webgl.force-layers-readback
webgl.force-index-validation
webgl.lose-context-on-memory-pressure
webgl.can-lose-context-in-foreground
webgl.max-contexts
webgl.max-contexts-per-principal
webgl.max-warnings-per-context
webgl.enable-draft-extensions
webgl.enable-privileged-extensions
webgl.disable-fail-if-major-performance-caveat
webgl.disable-DOM-blit-uploads
webgl.allow-fb-invalidation
webgl.perf.max-warnings
webgl.perf.max-acceptable-fb-status-invals
webgl.perf.spew-frame-allocs
webgl.angle.try-d3d11
webgl.angle.force-d3d11
webgl.angle.force-warp
webgl.dxgl.enabled
webgl.dxgl.needs-finish
layers.bench.enabled
layers.gpu-process.max_restarts
layers.acceleration.draw-fps
layers.deaa.enabled
layers.dump
layers.dump-texture
layers.dump-decision
layers.dump-client-layers
layers.dump-host-layers
layers.draw-borders
layers.draw-tile-borders
layers.draw-bigimage-borders
layers.child-process-shutdown
layers.max-active
layers.offmainthreadcomposition.frame-rate
layers.single-tile.enabled
layers.low-precision-buffer
layers.progressive-paint
layers.tiles.retain-back-buffer
layers.tiles.edge-padding
layers.draw-mask-debug
gfx.content.always-paint
gfx.apitrace.enabled
widget.window-transforms.disabled
gfx.direct2d.destroy-dt-on-paintthread
gfx.direct3d11.use-double-buffering
layers.shared-buffer-provider.enabled
dom.vr.autoactivate.enabled
dom.vr.controller_trigger_threshold
dom.vr.external.notdetected.timeout
dom.vr.external.quit.timeout
dom.vr.navigation.timeout
dom.vr.oculus.present.timeout
dom.vr.oculus.invisible.enabled
dom.vr.controller.enumerate.interval
dom.vr.display.enumerate.interval
dom.vr.inactive.timeout
dom.vr.poseprediction.enabled
dom.vr.require-gesture
dom.vr.puppet.enabled
dom.vr.display.rafMaxDuration
network.traffic_analyzer.enabled
dom.meta-viewport.enabled
layers.mlgpu.enable-on-windows7
layers.omtp.release-capture-on-main-thread
layers.omtp.dump-capture
fission.preserve_browsing_contexts

We want to avoid duplicate prefs between StaticPrefList.yaml and all.js. If there is any case where a pref must be defined in both files, these could be added to the ignore_prefs list in lintpref.

Removes the duplicate accessibility.* pref from all.js and 10 apz.* prefs. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes 10 apz.* prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes 10 apz.* duplicate prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes 10 duplicate apz.* prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes 10 duplicate apz.* prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes 10 duplicate prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes 9 duplicate prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes the 15 duplicate browser.* prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes the duplicate clipboard., devtools., and fission.* prefs, excluding fission.autostart, devtools.console.stdout.chrome, and devtools.console.stdout.content. These prefs are explicitly noted in all.js to remain in both files, so they will be added to ignore_prefs.

Removes 10 duplicate dom.* prefs from all.js. Imports comments from all.js.

Removes the 9 remaining dom.* duplicate prefs. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes 10 duplicate general.* prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes the last 12 duplicate general.* prefs. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes 10 duplicate gfx.* prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes duplicate gfx.* prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes the remaining 7 duplicate gfx.* prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

You have 16 patches and I guess you're about halfway through the de-duplication. I suggest landing the patches you have and then moving on to the remaining duplicate prefs, either in this bug or another bug. Waiting to land increases the likelihood you'll have conflicts with other changes, and landing in smaller chunks is also less risky.

https://hg.mozilla.org/mozilla-central/rev/bda91157c796
https://hg.mozilla.org/mozilla-central/rev/03abd948a887
https://hg.mozilla.org/mozilla-central/rev/cbbfb921b004
https://hg.mozilla.org/mozilla-central/rev/c7d99e47d3e8
https://hg.mozilla.org/mozilla-central/rev/bf87ad8885be
https://hg.mozilla.org/mozilla-central/rev/c1fe8c2c0a0f
https://hg.mozilla.org/mozilla-central/rev/7deecbbc45df
https://hg.mozilla.org/mozilla-central/rev/9fffc1ffc199
https://hg.mozilla.org/mozilla-central/rev/e14cef561be1
https://hg.mozilla.org/mozilla-central/rev/5b67dc7b4574
https://hg.mozilla.org/mozilla-central/rev/8e230fa660a1
https://hg.mozilla.org/mozilla-central/rev/6b07a9592c6c
https://hg.mozilla.org/mozilla-central/rev/5360c5642752
https://hg.mozilla.org/mozilla-central/rev/6f41b25d803a
https://hg.mozilla.org/mozilla-central/rev/49641a88b935
https://hg.mozilla.org/mozilla-central/rev/4c0f352d8a3c

Removes all duplicate gl.* prefs and 5 duplicate image.* prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes the remaining 11 image.* prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes 1 duplicate javascript.* and 9 layers.* prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Remove 12 duplicate layers.* prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes the remaining 7 duplicate layers.* prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes 11 duplicate layout.* prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes the remaining 10 duplicate layout.* prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes the 14 duplicate media.* prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes all of the duplicate mousewheel., nglayout., and network.* prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes all the duplicate privacy., security., toolkit., and widget. prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

Removes 10 duplicate webgl.* prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed.

Removes 10 duplicate webgl.* prefs. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed.

Removes duplicate webgl.* prefs from all.js. Replaces default values in StaticPrefList.yaml with their all.js counterparts where needed. Imports comments from all.js.

(In reply to Nicholas Nethercote [:njn] from comment #17)

You have 16 patches and I guess you're about halfway through the de-duplication. I suggest landing the patches you have and then moving on to the remaining duplicate prefs, either in this bug or another bug. Waiting to land increases the likelihood you'll have conflicts with other changes, and landing in smaller chunks is also less risky.

Good idea. Since all the prefs to be removed are already documented in the bug description I kept it all contained in this bug.

Backed out for bustages on StaticPrefList.yaml

backout: https://hg.mozilla.org/integration/autoland/rev/c7fa31dc1424a3b1aeb69c0953fde715d75d5dea

push: https://treeherder.mozilla.org/#/jobs?repo=autoland&group_state=expanded&revision=2d9dd627ef3c53cce68c40eb64f0602fc6416956&searchStr=build

failure log: https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=264985215&repo=autoland&lineNumber=3481

[task 2019-09-04T17:55:39.005Z] 17:55:39 INFO - make[2]: Entering directory '/builds/worker/workspace/build/src/obj-firefox/modules/libpref'
[task 2019-09-04T17:55:39.006Z] 17:55:39 INFO - modules/libpref/StaticPrefListAll.h.stub
[task 2019-09-04T17:55:39.006Z] 17:55:39 INFO - /builds/worker/workspace/build/src/obj-firefox/_virtualenvs/init/bin/python -m mozbuild.action.file_generate /builds/worker/workspace/build/src/modules/libpref/init/generate_static_pref_list.py emit_code init/StaticPrefListAll.h .deps/init/StaticPrefListAll.h.pp .deps/init/StaticPrefListAll.h.stub /builds/worker/workspace/build/src/modules/libpref/init/StaticPrefList.yaml
[task 2019-09-04T17:55:39.006Z] 17:55:39 ERROR - Traceback (most recent call last):
[task 2019-09-04T17:55:39.006Z] 17:55:39 INFO - File "/usr/lib/python2.7/runpy.py", line 162, in _run_module_as_main
[task 2019-09-04T17:55:39.006Z] 17:55:39 INFO - "main", fname, loader, pkg_name)
[task 2019-09-04T17:55:39.006Z] 17:55:39 INFO - File "/usr/lib/python2.7/runpy.py", line 72, in _run_code
[task 2019-09-04T17:55:39.006Z] 17:55:39 INFO - exec code in run_globals
[task 2019-09-04T17:55:39.006Z] 17:55:39 INFO - File "/builds/worker/workspace/build/src/python/mozbuild/mozbuild/action/file_generate.py", line 121, in <module>
[task 2019-09-04T17:55:39.007Z] 17:55:39 INFO - sys.exit(main(sys.argv[1:]))
[task 2019-09-04T17:55:39.007Z] 17:55:39 INFO - File "/builds/worker/workspace/build/src/python/mozbuild/mozbuild/action/file_generate.py", line 71, in main
[task 2019-09-04T17:55:39.007Z] 17:55:39 INFO - ret = module.dict[method](output, *args.additional_arguments, **kwargs)
[task 2019-09-04T17:55:39.007Z] 17:55:39 INFO - File "/builds/worker/workspace/build/src/modules/libpref/init/generate_static_pref_list.py", line 354, in emit_code
[task 2019-09-04T17:55:39.007Z] 17:55:39 INFO - pp.do_include(pref_list_filename)
[task 2019-09-04T17:55:39.007Z] 17:55:39 INFO - File "/builds/worker/workspace/build/src/python/mozbuild/mozbuild/preprocessor.py", line 836, in do_include
[task 2019-09-04T17:55:39.007Z] 17:55:39 INFO - self.handleLine(l)
[task 2019-09-04T17:55:39.007Z] 17:55:39 INFO - File "/builds/worker/workspace/build/src/python/mozbuild/mozbuild/preprocessor.py", line 583, in handleLine
[task 2019-09-04T17:55:39.008Z] 17:55:39 INFO - cmd(args)
[task 2019-09-04T17:55:39.008Z] 17:55:39 INFO - File "/builds/worker/workspace/build/src/python/mozbuild/mozbuild/preprocessor.py", line 628, in do_if
[task 2019-09-04T17:55:39.008Z] 17:55:39 INFO - raise Preprocessor.Error(self, 'SYNTAX_ERR', args)
[task 2019-09-04T17:55:39.008Z] 17:55:39 INFO - mozbuild.preprocessor.Error: ('$SRCDIR/modules/libpref/init/StaticPrefList.yaml', 4218, 'SYNTAX_ERR', '(defined(XP_WIN) || defined(MOZ_WIDGET_GTK)) && defined(NIGHTLY_BUILD)')
[task 2019-09-04T17:55:39.008Z] 17:55:39 INFO - backend.mk:233: recipe for target '.deps/init/StaticPrefListAll.h.stub' failed
[task 2019-09-04T17:55:39.008Z] 17:55:39 ERROR - make[2]: *** [.deps/init/StaticPrefListAll.h.stub] Error 1
[task 2019-09-04T17:55:39.009Z] 17:55:39 INFO - make[2]: Leaving directory '/builds/worker/workspace/build/src/obj-firefox/modules/libpref'
[task 2019-09-04T17:55:39.009Z] 17:55:39 INFO - /builds/worker/workspace/build/src/config/recurse.mk:101: recipe for target 'modules/libpref/export' failed
[task 2019-09-04T17:55:39.009Z] 17:55:39 ERROR - make[1]: *** [modules/libpref/export] Error 2
[task 2019-09-04T17:55:39.009Z] 17:55:39 INFO - make[1]: *** Waiting for unfinished jobs....

(In reply to Natalia Csoregi [:nataliaCs] from comment #35)

[task 2019-09-04T17:55:39.008Z] 17:55:39 INFO - raise Preprocessor.Error(self, 'SYNTAX_ERR', args)
[task 2019-09-04T17:55:39.008Z] 17:55:39 INFO - mozbuild.preprocessor.Error: ('$SRCDIR/modules/libpref/init/StaticPrefList.yaml', 4218, 'SYNTAX_ERR', '(defined(XP_WIN) || defined(MOZ_WIDGET_GTK)) && defined(NIGHTLY_BUILD)')

Hahh, I probably should have checked if that change was actually buildable...

https://hg.mozilla.org/mozilla-central/rev/470cb94addc6
https://hg.mozilla.org/mozilla-central/rev/b91fc532daf7
https://hg.mozilla.org/mozilla-central/rev/11298edb9b22
https://hg.mozilla.org/mozilla-central/rev/77e62e6bbeee
https://hg.mozilla.org/mozilla-central/rev/9e7f03846b91
https://hg.mozilla.org/mozilla-central/rev/9809406599b9
https://hg.mozilla.org/mozilla-central/rev/bba1a05ffa6b
https://hg.mozilla.org/mozilla-central/rev/008f549f420a
https://hg.mozilla.org/mozilla-central/rev/3d2b61921830
https://hg.mozilla.org/mozilla-central/rev/ba9ee276d4b4
https://hg.mozilla.org/mozilla-central/rev/a63c21ffa1d4
https://hg.mozilla.org/mozilla-central/rev/6ca0ddb7c9fd
https://hg.mozilla.org/mozilla-central/rev/78915f3b572b

this commit changed webgl.dxgl.enabled from default true in Windows to default false. Don't know if that was intended or not. Just FYI

That's correct: a63c21ffa1d4 is the revision that changed it.

Thanks for the report, Anna, that's a good catch. Can I ask how you discovered this?

I create Firefox Preferences diffs for a user.js project and webgl.dxgl.enabled used to be a "pref of interest" (until it was recently dropped from the user.js)

(In reply to Anna from comment #39)

this commit changed webgl.dxgl.enabled from default true in Windows to default false. Don't know if that was intended or not. Just FYI

Thank you for catching that! It should default to true on Windows.