I've updated to 2.13.3 and don't have the same problem, but I am guessing it's a related problem, so thought this might be a good spot to mention it.
For me, when I try going to the view admin page in firefox I don't have a problem with zoom, but the login doesn't work. If I hit the login button it doesn't do anything at all. Doing the same thing in Chrome from the same machine works fine.
I am also having various issues with Firefox addons. The biggest one for us is that we use Lastpass Enterprise in our company. The lastpass firefox addon will either not work at all, or it will "forget" the username and password. So every time the user opens firefox they have to reenter everything. Again, we don't have this issue with the lastpass addon for chrome on the same machine.
My suspicion is that it has something to do with the locations firefox and chrome are selecting to store the user profile.
If you go to about:profiles in firefox you'll likely see that it's selected a location under C:\SnapVolumesTemp\mountpoints\ to store the profile. From my experience, even if you change this to the "real" location it will switch itself back.
By comparison if you go to chrome://version in chrome you'll see that it's using a regular path under C:\Users\
