I found this on the console while starting firefox binary on arm: Crash Annotation GraphicsCriticalError: |[0][GFX1-]: glxtest: libpci missing (t=11.9489) [GFX1-]: glxtest: libpci missing it might be that the firefox binary tries to detect the gpu via libpci.so, providing the lib via emerging sys-apps/pciutils silences the crash annotation.
It's optional and not required, https://bugzilla.mozilla.org/show_bug.cgi?id=1676883