Crash report: https://crash-stats.mozilla.org/report/index/738e63c2-e080-4a14-a4de-f6f310210217

Reason: EXCEPTION_ACCESS_VIOLATION_READ

Top 10 frames of crashing thread:

0 xul.dll unscaled_composite gfx/wr/swgl/src/composite.h:403
1 xul.dll Composite gfx/wr/swgl/src/composite.h:449
2 xul.dll swgl::swgl_fns::LockedResource::composite gfx/wr/swgl/src/swgl_fns.rs:2426
3 xul.dll webrender::compositor::sw_compositor::SwCompositeThread::process_job gfx/wr/webrender/src/compositor/sw_compositor.rs:678
4 xul.dll webrender::compositor::sw_compositor::SwCompositeThread::wait_for_composites gfx/wr/webrender/src/compositor/sw_compositor.rs:832
5 xul.dll webrender::compositor::sw_compositor::{{impl}}::end_frame gfx/wr/webrender/src/compositor/sw_compositor.rs:1756
6 xul.dll webrender::renderer::Renderer::render_impl gfx/wr/webrender/src/renderer/mod.rs:2291
7 xul.dll webrender::renderer::Renderer::render gfx/wr/webrender/src/renderer/mod.rs:1890
8 xul.dll webrender_bindings::bindings::wr_renderer_render gfx/webrender_bindings/src/bindings.rs:637
9 xul.dll mozilla::wr::RendererOGL::UpdateAndRender gfx/webrender_bindings/RendererOGL.cpp:186

We first saw this with 20210112095256; the most interesting bug I noticed in near builds was bug 1679215.

This may be related to bug 1697306 and bug 1696025. We'll see if those make a difference here over time, but as of yet this is not high volume enough to be concerning.