I noticed today that a slider and gallery we are using (requiring jQuery) do not work in Firefox, they don’t get shown. Firefox’ console shows an error, that jQuery is not defined.
I removed all minify options and disable minify completely in W3 plugin. Everything works fine in Chrome though.
Found the issue, for anyone else with that problem (If you are using cloudflare):
A page rule broke that for me, I had a page rule for the home-page. After I disabled it, it works fine.