how to add firefox themes?!

[suskewiet]

I can't find any way to add a theme to firefox. I know it should be under Add-ons but for theme there is no button to install or find new themes. In thunderbird however there's no problem...
Firefox is using the gtk theme now which doesn't work properly so I really need to change the theme.

Any help?

[Cryovac]

You can install them via the Firefox theme website?

[suskewiet]

OK thx, wasn't aware of that!