Hi,
I had the same problem, and I believe it is caused by the recent move to GTK3. You can confirm that by playing around with the gtk3-demo app. Just run it for a minute and randomly click/run stuff in there.
As a workaround, there is a firefox-gtk2 package in the AUR (takes some hours to compile, but the -bin version is buggy).
Here is a stack trace of the gtk3-demo crashing with the same error, unfortunately I don't have debug builds, but XIGetClientPointer doesn't work the way gtk3 calls it somehow.
(gtk3-demo:6305): Gdk-ERROR **: The program 'gtk3-demo' received an X Window System error. This probably reflects a bug in the program. The error was 'BadRequest (invalid request code or no such operation)'. (Details: serial 21589 error_code 1 request_code 131 (XInputExtension) minor_code 45) (Note to programmers: normally, X errors are reported asynchronously; that is, you will receive the error a while after causing it. To debug your program, run it with the GDK_SYNCHRONIZE environment variable to change this behavior. You can then get a meaningful backtrace from your debugger if you break on the gdk_x_error() function.)
Thread 1 "gtk3-demo" received signal SIGTRAP, Trace/breakpoint trap. 0x00007ffff55517eb in g_logv () from /usr/lib/libglib-2.0.so.0 (gdb) bt #0 0x00007ffff55517eb in g_logv () from /usr/lib/libglib-2.0.so.0 #1 0x00007ffff555195f in g_log () from /usr/lib/libglib-2.0.so.0 #2 0x00007ffff7276ad8 in ?? () from /usr/lib/libgdk-3.so.0 #3 0x00007ffff7282ca9 in ?? () from /usr/lib/libgdk-3.so.0 #4 0x00007ffff4a4187d in _XError () from /usr/lib/libX11.so.6 #5 0x00007ffff4a3e7c7 in ?? () from /usr/lib/libX11.so.6 #6 0x00007ffff4a3f935 in _XReply () from /usr/lib/libX11.so.6 #7 0x00007ffff47f11d4 in XIGetClientPointer () from /usr/lib/libXi.so.6 #8 0x00007ffff7275627 in ?? () from /usr/lib/libgdk-3.so.0 #9 0x00007ffff781ca4d in ?? () from /usr/lib/libgtk-3.so.0 #10 0x00007ffff781cfe4 in ?? () from /usr/lib/libgtk-3.so.0 #11 0x00007ffff7246988 in ?? () from /usr/lib/libgdk-3.so.0 #12 0x00007ffff554b823 in ?? () from /usr/lib/libglib-2.0.so.0 #13 0x00007ffff554adba in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0 #14 0x00007ffff554b160 in ?? () from /usr/lib/libglib-2.0.so.0 #15 0x00007ffff554b20c in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0 #16 0x00007ffff6b14afd in g_application_run () from /usr/lib/libgio-2.0.so.0 #17 0x00000000004154cc in main () (gdb)
Regards,
U.M.G.