It looks like Firefox currently uses the software fallback for Webrender when looking at about:support. (It says “Webrender (software)” next to “Compositing”)
Anyone know the reason? Webrender should be substantially faster than its software fallback.
Likely because the Librem5 GPU doesn’t support features needed by WebRender.
Just skimming here
https://searchfox.org/mozilla-release/source/widget/gtk/GfxInfo.cpp
and I happened to notice that Firefox’s about:config page appends a new key/value pair, just for me 
“gfx.blacklist.webrender.failureid”: “FEATURE_FAILURE_OPENGL_LESS_THAN_3”
Anyone know what the status is of GLES 3 in etnaviv?
You have up to date information on OpenGL/GLES, OpenCL, and Vulkan support in Mesa here: https://mesamatrix.net/