You should be able to adjust the defaults in the configuration of your FireFox browser. That includes map links and should be relatively easy to do. Google is still your friend.
However, if you can't or the botched installation made a mess of many more settings than just maps, try and look for a button to reset your configuration of FireFox to 'default', 'original default' or something similar. Make sure you create a backup of your current configuration first (MozBack, if I remember correctly)!
You can also create a new user profile in FireFox and manually copy things from your old profile into the new one. The latter options do not sound like fun and they aren't.
Consider it a lesson learned regarding installing software that has been dreamed up by Apple. Should not be allowed to be installed on anything that isn't Apple hardware, as those users are accustomed to the 'Apple's way or the highway'-mentality that comes with their software. There are more than enough video-cutters that are based on ffMpeg, which is excellent video manipulation software by itself. Although it has a steep learning curve in that form. But there are many (freeware)solutions that make working with ffMpeg a lot easier.