[hipsterstal1n]

This is just flat out wrong. I am on regular Firefox and can install extensions from files.

See: https://support.mozilla.org/en-US/kb/find-and-install-add-on... and look under "How do I find and install add-ons?" > "For Advanced User"

[eviks]

Nope

> You can also install a signed add-on from a file

This means that unlike Chrome Firefox doesn't support the simple case of downloading an extension repo, tweaking a few things, and loading it