Bug 1476405: Part 5 - Create nsThread wrapper and use reasonable stack size for BackgroundHangMonitor. r?erahm BackgroundHangMonitor is a special snowflake, and uses PR_CreateThread directly, for some reason. MozReview-Commit-ID: 2Qg28EqDwM7

Bug 1476405: Part 4 - Create nsThread wrappers whenever a thread is registered with the profiler. r?erahm,mstange This automatically gets us wrappers (and therefore memory statistics) for Stylo threads, JS HelperThreads, and any other non-nsThread threads that we already register with the profiler. MozReview-Commit-ID: 8ZPjb0ojyWp

Bug 1476405: Part 3 - Use reasonable stack sizes and create wrappers for JS threads. r?erahm,tcampbell For ordinary JS helper threads, we can update names and create wrappers using the existing thread profiler hooks, but we still need to update their default stack sizes to avoid huge pages. For the XPConnect JS Watchdog thread, we sometimes get a wrapper as it is, but only sometimes. And we never use a reasonable stack size. MozReview-Commit-ID: EuR3gL5JATL

Bug 1476405: Part 2b - Use default thread size from nsIThreadManager in Linux PlatformThreads. r?jld MozReview-Commit-ID: 4Mod1IdzJBw

Bug 1476405: Part 2a - Create nsThread wrappers/set names for chromium threads. r?erahm,jld MozReview-Commit-ID: FvGhq6nhIde

Bug 1476405: Part 1 - Allow enumerating non-native nsThread threads. r=erahm MozReview-Commit-ID: 1JKxWeejqzi

Bug 1474529 - Update scalar is_devtools_user to opt-out and expire in Fx66;r=francois MozReview-Commit-ID: 2gSYSEnvCPN

Bug 1443923 - part9: Listen to "customelementdefined" in inspector actor;r=bgrins MozReview-Commit-ID: 5VLwHGaWJLu

Bug 1443923 - part8: Emit chrome-only event customelementdefined for DevTools;r=masayuki MozReview-Commit-ID: GCFhhpVj5VS

Bug 1443923 - part7: Use InspectorUtils.isCustomElementName in inspector actor;r=bgrins MozReview-Commit-ID: 9aKFGcoX8TS

Bug 1443923 - part6: Expose isCustomElementName to DevTools via InspectorUtils;r=emilio MozReview-Commit-ID: GaHP1gOCwoB

Bug 1477254: Assert that varcache prefs match pref values at content process startup. r?njn In order to avoid the overhead of doing a full pref lookup for every static var cache at content process startup, we currently assume that the default value of any static varcache pref will always match the default value of its database entry (as long as the pref isn't locked). This lets us only perform lookups for preferences which have a user value, or are locked. If the default values of those preferences are changed in a bundled preference file, though, the varcache value will be correct in the parent process, but not in child processes. Since this is an easy mistake to make, we should assert that it doesn't happen. Note: This change only affects applications which use e10s. Applications like Thunderbird can still override default values of any static pref with impunity. Repacks and distributors can only do so by changing user values or locking the preference after the change (which is the standard practice for enterprise deployments). MozReview-Commit-ID: JMHQBrp9HN

Bug 1476975 - P3. Fix canPlayType/isTypeSupported for AV1 content. r=dminor AV1 support is behind a pref, as such, the result of canPlayType should depends on the value of that pref. Additionally to this change we remove AOMDecoder::IsSupportedCodec as it implied confusion on what a codec mimetype is. There are two type of codec mimetype: the one describing the container content ("av1") and the one describing the codec itself "video/av1") AOMDecoder shouldn't know anything about containers (e.g. mp4 or webm)

Bug 1476975 - P2. Add mochitests. r=dminor

Bug 1476975 - P1. Make media.av1.enabled pref public. r=dminor Makes it easier to toggle for tests.

Bug 1465616 - Add a mochitest for fixed position hit-testing. r=botond MozReview-Commit-ID: IC82JZoVgPs

Bug 1465616 - Add reftests for fixed and sticky elements. r=botond MozReview-Commit-ID: IzSUQqvjrUp

Bug 1465616 - Use layout viewport size to compute visible rect for fixed position elements. r?mstange Since fixed position elements are now scrollable, we need to ensure that they're drawn using the layout viewport size instead of only the SPC-SPS, since otherwise they'd appear to be clipped when scrolled. MozReview-Commit-ID: 4p3pWnwluvz

Bug 1465616 - Remove call to AlignFixedAndStickyLayers for RCD-RSF. r=botond MozReview-Commit-ID: B8HH6mbjTnv

Bug 1465616 - Don't use SPC-SPS to layout fixed position elements. r=mstange MozReview-Commit-ID: 5D4ErVFx8Bm