Sometimes you may find certain features of firefox not working after installing or upgrading some software relating to firefox. It could be the forward and back button suddenly greyed out, out certain icons dissapeared…etc.
The problem is 99% due to permission issues. Because you often have to be root to install or upgrade firefox, the permission of certain mozilla files are left at root after the upgrade. What you need to do is to change the permission back to yourself and you fixed the problem.
As mentioned in my previous firefox websearch error blog, the fix is as easy as
sudo chown username:username -R ~/.mozilla/firefox