Themes are somehow able to crash firefox.
I have no idea what is going on, but I filed this bug report: https://github.com/paullinuxthemer/Telinkrin-GTK/issues/14 on the Telinkrin-GTK theme. Somehow, the theme is able to crash firefox on startup, at least on my machine (running arch linux). This seems like a problem that GNOME should prevent, since, I assume, gtk themes should not be able to cause application to crash. I am not sure if this is the correct part of GNOME to report on, but I have no idea which part is causing the problem.