Found with m-c 20220108-4531cca1d7f9
This is periodically triggered on start up with an UBSan build. To enable this check add the following to your mozconfig:

ac_add_options --enable-undefined-sanitizer="function"

Note the build is blocked on bug 1747298 which has a pending fix.

src/program.h:80:5: runtime error: call to function cs_clip_rectangle_vert::set_uniform_matrix4fv(cs_clip_rectangle_vert*, int, float const*) through pointer to incorrect function type 'void (*)(glsl::VertexShaderImpl *, int, const float *)'
src/objdir-ff-ubsan/x86_64-unknown-linux-gnu/release/build/swgl-81e23a6b5b5d5a82/out/cs_clip_rectangle.h:556: note: cs_clip_rectangle_vert::set_uniform_matrix4fv(cs_clip_rectangle_vert*, int, float const*) defined here
    #0 0x7fa55feb4b3e in set_uniform_matrix4fv src/gfx/wr/swgl/src/program.h:80:5
    #1 0x7fa55feb4b3e in UniformMatrix4fv src/gfx/wr/swgl/src/gl.cc:2056:20
    #2 0x7fa55ecb7419 in webrender::device::gl::Device::set_uniforms::h78c841e6892a6471 src/gfx/wr/webrender/src/device/gl.rs:3003:9
    #3 0x7fa55faec75c in webrender::renderer::shade::LazilyCompiledShader::bind::hd58153f3360f20ee src/gfx/wr/webrender/src/renderer/shade.rs:162:13
    #4 0x7fa55f1f34e4 in webrender::renderer::Renderer::draw_clip_batch_list::hda5fb94d123098c4 src/gfx/wr/webrender/src/renderer/mod.rs:3738:13
    #5 0x7fa55f1fdb5d in webrender::renderer::Renderer::draw_alpha_target::hc8f2f66a6e80148d src/gfx/wr/webrender/src/renderer/mod.rs:3970:13
    #6 0x7fa55f1fdb5d in webrender::renderer::Renderer::draw_frame::hd5decbfd2239f2cf src/gfx/wr/webrender/src/renderer/mod.rs:4745:17
    #7 0x7fa55f1df7aa in webrender::renderer::Renderer::render_impl::he0ece11432c9a6eb src/gfx/wr/webrender/src/renderer/mod.rs:2002:17
    #8 0x7fa55f1dc607 in webrender::renderer::Renderer::render::hee7ce0b8d1719409 src/gfx/wr/webrender/src/renderer/mod.rs:1724:30
    #9 0x7fa55ea49abd in wr_renderer_render src/gfx/webrender_bindings/src/bindings.rs:622:11
    #10 0x7fa54e5dd042 in mozilla::wr::RendererOGL::UpdateAndRender(mozilla::Maybe<mozilla::gfx::IntSizeTyped<mozilla::gfx::UnknownUnits> > const&, mozilla::Maybe<mozilla::wr::ImageFormat> const&, mozilla::Maybe<mozilla::Range<unsigned char> > const&, bool*, mozilla::wr::RendererStats*) src/gfx/webrender_bindings/RendererOGL.cpp:185:8
    #11 0x7fa54e5db4b4 in mozilla::wr::RenderThread::UpdateAndRender(mozilla::wr::WrWindowId, mozilla::layers::BaseTransactionId<mozilla::VsyncIdType> const&, mozilla::TimeStamp const&, bool, mozilla::Maybe<mozilla::gfx::IntSizeTyped<mozilla::gfx::UnknownUnits> > const&, mozilla::Maybe<mozilla::wr::ImageFormat> const&, mozilla::Maybe<mozilla::Range<unsigned char> > const&, bool*) src/gfx/webrender_bindings/RenderThread.cpp:516:31
    #12 0x7fa54e5da1f3 in mozilla::wr::RenderThread::HandleFrameOneDoc(mozilla::wr::WrWindowId, bool) src/gfx/webrender_bindings/RenderThread.cpp:368:3
    #13 0x7fa54e605676 in apply<mozilla::wr::RenderThread, void (mozilla::wr::RenderThread::*)(mozilla::wr::WrWindowId, bool)> src/objdir-ff-ubsan/dist/include/nsThreadUtils.h:1153:12
    #14 0x7fa54e605676 in mozilla::detail::RunnableMethodImpl<mozilla::wr::RenderThread*, void (mozilla::wr::RenderThread::*)(mozilla::wr::WrWindowId, bool), true, (mozilla::RunnableKind)0, mozilla::wr::WrWindowId, bool>::Run() src/objdir-ff-ubsan/dist/include/nsThreadUtils.h:1200:13
    #15 0x7fa54ac49434 in nsThread::ProcessNextEvent(bool, bool*) src/xpcom/threads/nsThread.cpp:1189:16
    #16 0x7fa54ac53a91 in NS_ProcessNextEvent(nsIThread*, bool) src/xpcom/threads/nsThreadUtils.cpp:467:10
    #17 0x7fa54c475ef4 in mozilla::ipc::MessagePumpForNonMainThreads::Run(base::MessagePump::Delegate*) src/ipc/glue/MessagePump.cpp:300:20
    #18 0x7fa54c274e82 in RunHandler src/ipc/chromium/src/base/message_loop.cc:324:3
    #19 0x7fa54c274e82 in MessageLoop::Run() src/ipc/chromium/src/base/message_loop.cc:306:3
    #20 0x7fa54ac4160e in nsThread::ThreadFunc(void*) src/xpcom/threads/nsThread.cpp:391:10
    #21 0x7fa57a9e56d3 in _pt_root src/nsprpub/pr/src/pthreads/ptthread.c:201:5
    #22 0x7fa57a62e6da in start_thread /build/glibc-S9d2JN/glibc-2.27/nptl/pthread_create.c:463
    #23 0x7fa57960c71e in __clone /build/glibc-S9d2JN/glibc-2.27/misc/../sysdeps/unix/sysv/linux/x86_64/clone.S:95