This could be bug 635134 comment 153:

Weston fails with GLXtest failed, unable to open connection to X server.

Seen on Socorro.
This bug is for crash report bp-21a7b235-743e-4a50-8a53-7ce2c0190601.

App Notes FP(D00-L1010-W00000100-T000) WR! WR+ OMTP? OMTP+4 Arch Linux
GLXtest process failed (exited with status 1): Unable to open a connection to the X server
EGL? EGL+ GL Context? GL Context+

MOZ_CRASH Reason (Sanitized) explicit panic

GraphicsCriticalError |[0][GFX1-]: Attempting to create a render task of size 28800x2400 (t=3.40008)

Top 10 frames of crashing thread:

0 libxul.so GeckoCrash toolkit/xre/nsAppRunner.cpp:5162
1 libxul.so gkrust_shared::panic_hook toolkit/library/rust/shared/lib.rs:243
2 libxul.so core::ops::function::Fn::call src/libcore/ops/function.rs:69
3 libxul.so std::panicking::rust_panic_with_hook src/libstd/panicking.rs:478
4 libxul.so std::panicking::begin_panic src/libstd/panicking.rs:408
5 libxul.so webrender::frame_builder::FrameBuilder::build_layer_screen_rects_and_cull_layers gfx/wr/webrender/src/render_task.rs:49
6 libxul.so webrender::frame_builder::FrameBuilder::build gfx/wr/webrender/src/frame_builder.rs:549
7 libxul.so webrender::render_backend::Document::build_frame gfx/wr/webrender/src/render_backend.rs:522
8 libxul.so webrender::render_backend::RenderBackend::update_document gfx/wr/webrender/src/render_backend.rs:1461
9 libxul.so webrender::render_backend::RenderBackend::process_api_msg gfx/wr/webrender/src/render_backend.rs:1307

I think this issue went away in 72, as the Linux panic went away. There are some isolated reports of it on Windows, but it is definitely a different problem than the one originally seen here. There are only two reports and the stack traces are not very useful for further investigation, so I will defer unless the problem worsens.