Steps: 1. Enable OMTC as per https://mozillagfx.wordpress.com/2012/10/06/how-to-help-testing-off-main-thread-compositing/ 2. Show the add-on manager, pick something like plug-ins with many items or shrink the window so that there is a scrollbar. 3. Scroll. The scrollable area disappears. Sandy bridge graphics on Ubuntu Quantal. { "application": { "name": "Firefox", "version": "19.0a1", "userAgent": "Mozilla/5.0 (X11; Linux x86_64; rv:19.0) Gecko/19.0 Firefox/19.0", "supportURL": "http://support.mozilla.org/1/firefox/19.0a1/Linux/en-US/" }, "modifiedPreferences": { "accessibility.typeaheadfind.flashBar": 0, "browser.cache.disk.capacity": 358400, "browser.cache.disk.smart_size.first_run": false, "browser.cache.disk.smart_size.use_old_max": false, "browser.cache.disk.smart_size_cached_value": 358400, "browser.places.smartBookmarksVersion": 4, "browser.startup.homepage_override.mstone": "19.0a1", "browser.startup.homepage_override.buildID": "20121013030542", "dom.mozApps.used": true, "extensions.lastAppVersion": "19.0a1", "layers.async-video.enabled": true, "layers.acceleration.draw-fps": true, "layers.acceleration.force-enabled": true, "layers.offmainthreadcomposition.animate-opacity": true, "layers.offmainthreadcomposition.animate-transform": true, "network.cookie.prefsMigrated": true, "places.history.expiration.transient_current_max_pages": 104858, "places.database.lastMaintenance": 1350208789, "privacy.sanitize.migrateFx3Prefs": true }, "graphics": { "numTotalWindows": 1, "numAcceleratedWindows": 0, "windowLayerManagerType": "Basic", "numAcceleratedWindowsMessage": [ "no information" ], "adapterDescription": "Intel Open Source Technology Center -- Mesa DRI Intel(R) Sandybridge Desktop ", "adapterVendorID": "Intel Open Source Technology Center", "adapterDeviceID": "Mesa DRI Intel(R) Sandybridge Desktop ", "adapterRAM": "", "adapterDrivers": "", "driverVersion": "3.0 Mesa 9.0", "driverDate": "", "webglRendererMessage": [ "no information" ], "info": { "AzureCanvasBackend": "cairo", "AzureFallbackCanvasBackend": "none", "AzureContentBackend": "none" } }, "javaScript": { "incrementalGCEnabled": true }, "accessibility": { "isActive": false, "forceDisabled": 0 }, "libraryVersions": { "NSPR": { "minVersion": "4.9.3 Beta", "version": "4.9.3 Beta" }, "NSS": { "minVersion": "3.14.0.0 Basic ECC Beta", "version": "3.14.0.0 Basic ECC Beta" }, "NSSUTIL": { "minVersion": "3.14.0.0 Beta", "version": "3.14.0.0 Beta" }, "NSSSSL": { "minVersion": "3.14.0.0 Basic ECC Beta", "version": "3.14.0.0 Basic ECC Beta" }, "NSSSMIME": { "minVersion": "3.14.0.0 Basic ECC Beta", "version": "3.14.0.0 Basic ECC Beta" } }, "userJS": { "exists": false }, "extensions": [ { "name": "Ubuntu Firefox Modifications", "version": "2.4.1", "isActive": false, "id": "ubufox@ubuntu.com" }, { "name": "Unity Desktop Integration", "version": "2.3.5", "isActive": false, "id": "webapps-team@lists.launchpad.net" }, { "name": "Unity Websites integration", "version": "2012.10.12.beta", "isActive": false, "id": "{2e1445b0-2682-11e1-bfc2-0800200c9a66}" } ] }

I can reproduce this bug. A quick look in gdb shows that we are trying to create a glx pixmap from an image which content type is gfxASurface::CONTENT_ALPHA here is a piece of backtrace: #0 mozilla::gl::GLXLibrary::CreatePixmap (this=0x7ffff783b120, aSurface=0x7fffcfc65d30) at /home/nico/dev/mozilla/mozilla-central/gfx/gl/GLContextProviderGLX.cpp:325 #1 0x00007ffff5345bc2 in mozilla::gl::GLContextGLX::CreateTextureImage (this=0x7fffdc349000, aSize=..., aContentType=gfxASurface::CONTENT_ALPHA, aWrapMode=33071, aFlags=mozilla::gl::TextureImage::ForceSingleTile) at /home/nico/dev/mozilla/mozilla-central/gfx/gl/GLContextProviderGLX.cpp:1095 #2 0x00007ffff53028b5 in mozilla::layers::ShadowImageLayerOGL::Init (this=0x7fffcfc61400, aFront=...) at /home/nico/dev/mozilla/mozilla-central/gfx/layers/opengl/ImageLayerOGL.cpp:719 #3 0x00007ffff5302f25 in mozilla::layers::ShadowImageLayerOGL::Swap (this=0x7fffcfc61400, aNewFront=..., aNewBack=0x7fffe01fddc0) at /home/nico/dev/mozilla/mozilla-central/gfx/layers/opengl/ImageLayerOGL.cpp:784 #4 0x00007ffff5336416 in mozilla::layers::ShadowLayersParent::RecvUpdate (this=0x7fffda16d940, cset=..., targetConfig=..., isFirstPaint=@0x7fffe01fe5ff: false, reply=0x7fffe01fe5f0) at /home/nico/de v/mozilla/mozilla-central/gfx/layers/ipc/ShadowLayersParent.cpp:447 in frame 2 (ShadowImageLayerOGL::Init), autoSurf.ContentType() returns gfxASurface::CONTENT_ALPHA If I step in the CreatePixmap code here: http://dxr.mozilla.org/mozilla-central/gfx/gl/GLContextProviderGLX.cpp#l331 I see that we never match an index (see: http://dxr.mozilla.org/mozilla-central/gfx/gl/GLContextProviderGLX.cpp#l386 ) because we always escape from the loop at line 331, with redMask, greenMask and blueMask always equal to zero. I don't know the GLX code very well so I don't have much to say about this at this point (is it just that we don't support creating a pixmap without r,g,b channels?) I am surprised that we try to swap an image of type "alpha" in an image layer (what would we do this for?) The bug happens concistently in about:addons but I haven't seen this anywhere else on the web so far.

Mass tracking-e10s flag change. Filter bugmail on "2be0fcce-e36a-4e2c-aa80-0e3d33eb5406".

(In reply to Nicolas Silva [:nical] from comment #1) > I am surprised that we try to swap an image of type "alpha" in an image > layer (what would we do this for?) The scrollable area has rounded corners, so we create an alpha-only mask layer for the scrolled layers which masks away the corners. The mask layer is an image layer.

I just retested this and it seems to be fixed. I used to be able to reproduce it.