Did you try to zoom out?

Try to rename/remove xulstore.json in the Firefox profile folder with Firefox closed.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Hello matek15,

Just in case the above doesn't solve the problem :

Type in the address bar about:config and press Enter (promise to be careful, if asked)

Type in the search bar and look for the preference :

privacy.resistFingerprinting and set its value to false

If you had to change the value, then close and restart Firefox.

Also see :

https://www.ghacks.net/2019/04/24/firefox-not-remembering-the-last-window-size-this-may-fix-it/

Thank you for responding, but I still cannot get FireFox to work. When I open it, the page comes up very large as if it is zoomed in very close. I cannot access the menu bar because the page loads at the bottom of the page and I am unable to scroll up to get to the menu bar. This is a new iMac I got last week, but FireFox had been working fine up until yesterday. On a unrelated note, the 5kPlayer on my Mac is now only playing audio, no video. This started about the same time as my FireFox issue. Thank you again, any help is greatly appreciated.