From Bugzilla Helper:
User-Agent: Mozilla/4.76 [en] (X11; U; Linux 2.4.2-0.1.19 i686)
If the usb driver is compiled as a module, but mousedev is compiled into
the kernel (i.e. not modular), a warning is issued on boot ("can't find
module mousedev", or similar) just after the usb module is loaded.
However, the usb mouse still works.
Reproducible: Didn't try
Don't do that then ;)