At that time there were some addons that worked to translate web (not just selected text), and at least one of them was even recommended by mozilla.

The problem is that to translate from google they used a remote code execution method, I’m not sure but I seem to remember that mozilla changed their policy to not allow that and didn’t warn the devs (if mozilla simply didn’t notice for years it would be even more worrying).
In any case someone reported them all and they were immediately banned, some of the devs tried to reason with mozilla and look for workarounds but to no avail.

Until alternatives appeared (after a couple of years?) it was necessary to install blacklisted or unsigned addons, which is a bit tedious.