Every time Firefox updates the user interface gets corrupted and I get half of it in English and the other half in Italian. See the attached image for an example of the problem. This problems seems to be similar to https://support.mozilla.org/en-US/questions/1274346 except that when I try to update the add-ons I always get the message that they're already up to date. Due to the frequency Firefox gets updated resetting it every time this happens as suggested in the previous answer is not an acceptable solution.