Form-input font is FontAwesome instead of Open Sans on Firefox

One-sentence description

If I open the edit profile page in Firefox (Mozilla Firefox 68.0.2 on Fedora 30) I see FontAwesome icons instead of a normal font.

Current behaviour / Reproducing the bug

  • Log in to Thalia.nu.
  • Click: Edit profile
  • Every input box has the FontAwesome font instead of the normal font.

thalia-bug

Expected behaviour

I should be seeing a normal font (Open Sans?). Just like on the rest of the site.

This is what I see as the computed CSS in the Firefox dev console thalia-bug-dev-console

The site is rendering properly on Chromium. It might be specific to my Firefox, but I have tested it on two machines (both Fedora) and both have the same problem.