Bug 843668 - Implement WebGL -draft- extension EXT_sRGB. r=jgilbert

https://www.khronos.org/registry/webgl/extensions/EXT_sRGB/
See content/canvas/test/webgl/conformance/extensions/ext-sRGB.html for example
usage.

OSX 10.6 has a failure when reading back the results from an sRGB format
texture attached to an FBO. Blacklist MacOSX 10.6 and all lower versions.
Bug 894658 - Implement ES6 Array.prototype.{keys,entries}. r=jorendorff
Bug 765285 - Include last 3 days of crash IDs in about:support: Improve localization comments. r=Mossop