The issue seems to be in a setting that has reset in your Firefox, affecting the forum view and the problem you have. I suggest that you make a backup of everything you have in your browser (bookmarks, passwords) and to remove browser by uninstall+delete Firefox folder. After that it would be good to clean your system with CCleaner (it is free tool), and then to install latest version of Firefox.
I am using the forum now for the Tor browser directly and it seems okay here. I think this one is the option I have not tried yet. I will give it a try. Thanks for your input.
I have tried the 2nd option with few more options those are available there. Anyway, I am on to reinstalling firefox.
Edit:
After reinstalling the Firefox and connecting the TOR again, I see everything is back to the normal. Thanks everyone for your input.
I am locking this topic.