>> крах подсистемы WebRender
> Это не та ли, что на расте?!

А ведь вместо газификации луж можно просто пройти по ссылке:

3 libgdk-3.so.0 _gdk_x11_display_error_event gdk/x11/gdkdisplay-x11.c:2766
4 libgdk-3.so.0 gdk_x_error gdk/x11/gdkmain-x11.c:260
5 libX11.so.6 _XError src/XlibInt.c:1503
6 libX11.so.6 handle_error src/xcb_io.c:207
7 libX11.so.6 _XReply src/xcb_io.c:793
8 libX11.so.6 XGetImage
9 libxul.so _get_image_surface gfx/cairo/cairo/src/cairo-xlib-surface.c:813
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>  WindowSurfaceX11Image::Commit uses DrawSurface(OP_OVER) to do the final blit from a gfxImageSurface to the window wrapped by a gfxXlibSurface. Cairo notices the OP_OVER and does an undesirable sequence of fallbacks - it does an XGetImage on the window to get the image data, blends to it, and then XPutImage's the result back to the window. So the XGetImage becomes bad for two reasons - 1) it can cause an X error, 2) it is causing a readback from the window server that we really don't want for performance reasons.
>