My unmodified Firefox stable channel on Linux has WebGL enabled OOTB and my distro does not have any specific flags specified for WebGL (or GL in general) in the package.
> GL layers acceleration is not yet enabled by default (see bug 594876). You can enable it by setting layers.acceleration.force-enabled=true in about:config.
That means off by default. Also maybe relevant is that I'm on the Firefox Graphics team so I have some knowledge of this.
If you want to verify, download a stock Firefox build from Mozilla, run it on a new profile, and check what it says for Compositing in the Graphics section. OpenGL means acceleration, Basic means software.
This page disagrees:
https://wiki.mozilla.org/Blocklisting/Blocked_Graphics_Drive...
My unmodified Firefox stable channel on Linux has WebGL enabled OOTB and my distro does not have any specific flags specified for WebGL (or GL in general) in the package.