Firefox Developers Still Hesitant About Using EGL Over GLX On X11 Linux
While Wayland support depends upon EGL and there has been EGL support within Mesa and the other graphics drivers on Linux for a number of years now, Firefox developers are still hesitant about shipping EGL support by default for Firefox on X11.
A Phoronix reader pointed out a bug report to us where Firefox developers are still apprehensive over using EGL by default for Firefox on Linux/X11, even though Mesa's EGL support has been relatively solid for years. There's a belief that the EGL performance is worse off than GLX, but at least some upstream Mesa developers don't believe that to be the case plus the fact most modern drivers relying upon GLAMOR with EGL/OpenGL for 2D acceleration.
There is this six year old Mozilla bug report about considering to use EGL by default on Linux. That bug report was spurred by this 2012 Phoronix article about the X.Org GLX support effectively being deprecated.
Six years later, GLX remains in a basically deprecated/maintenance state with not many improvements and most encouraging the use of EGL as the windowing system API these days. But even in 2018, plenty of software is still shipping dependent upon GLX exclusively while there are also more projects these days to allow the dynamic selection of EGL/GLX at run-time, like Waffle.
Martin Stransky who is the Firefox maintainer at Red Hat recently commented though, "EGL/Mesa performance on X11 is poor relatively to GLX implementation so it does not make sense to ship EGL/X11 builds [of Firefox] on Linux."
The problem with not shipping the EGL default is that Firefox's EGL/GLX selection is done at build-time rather than run-time. This leaves basically the last major blocker to Firefox's Wayland support in either needing to go ahead with EGL on X11 or make it possible to provide run-time switching to offer GLX on X11 and EGL on Wayland.
No decision has been made yet as what Firefox will end up doing about EGL Linux support, but when a consensus has reached, you can expect to hear about it on Phoronix.