We detected a 50KB regression in the base content JS measure [1] after bug 1473595 landed (this was masked by a 100KB improvement that landed afterwards on m-c). Kris indicated this is probably due to eagerly loading screenshot-related code when loading a tab. It would be helpful to understand this regression and possibly pursue a backout (or revert the pref to false) if we don't have time to look into it. Note: to reproduce you'll need to run in a clean profile, the awsy base test can be run locally with: > ./mach awsy-test testing/awsy/awsy/test_base_memory_usage.py and on try with > ./mach try -b o -p linux64 -u awsy-base-e10s --rebuild 5 [1] https://treeherder.mozilla.org/perf.html#/compare?originalProject=mozilla-central&newProject=autoland&newRevision=9fe3f733a48a0c662fd5a3b60195bdeb16c5846d&framework=4&filter=js&selectedTimeRange=172800

(In reply to Eric Rahm [:erahm] from comment #0) > Kris indicated this is probably due to eagerly loading > screenshot-related code when loading a tab. That's correct. We automatically generate thumbnails after session restore, and after switching away from a tab. We can probably stop doing both things since generating thumbnails on the fly is fast enough for the limited number of previews we're dealing with here.

Pushed by cbrindusan@mozilla.com: https://hg.mozilla.org/integration/mozilla-inbound/rev/033d948a9332 Stop eagerly creating thumbnails for the Ctrl+Tab panel. r=jaws