Try the following:
(1) Download the latest Firefox version for your computer from Mozilla. Make a backup of your Bookmarks / Favorite links.
Then uninstall and reinstall Firefox. After uninstalling Firefox and before reinstalling it, restart the Computer and open the file explorer. Click on the three dots at the extreme right of the Explorer menu bar. Click on "Options" and in the window that opens, go to the "View" tab. In the list find "Hide protected system files". Uncheck it.
Then go to your user folder in explorer. You will see more folders and files than normaly, but the newly visible folders and files are a bit "foggy", like half-hidden. Find the folder "App Data" (not Application Data") and open the folder. You will see three sub-folders "Local", "LocalLow" and "Roaming". In "Local" and "Roaming" there will be "Mozilla" folders. Simply delete them. Then you can put the tick back in front of "Hide protected system files"; in general be carefull with these hidden files and folders, ... (but not in this case for the Mozilla folders).
Restart and reinstall Firefox. You will need to set back all your settings in Firefox, give in your passwords again, and reimport your bookmarks / favorites.
(2) Do you have "U-block origin" installed, a firefox extension ? If I would be allowed to only have one extension in Firefox, it would be this one. Open Firefox and find "Extensions and Settings" on the left side of your Firefox window. In the search bar (top right) tape "U-block origin". Install the extension. Restart Firefox. Go back to "Extensions" find "U-Block origin" and click on the three dots (right). Click on "Options", you will land on a tab called "Filter list". Tick everything you can on the list in this tab. Please pay also attention to the small arrows / triangles on the left of the list entries, click on them and also tick the boxes in these sub-folders. Also tick all the regions / countries, even if you never have the intention to go there (you never know where you are sent by a link). Finally click on "Update" (or similar = middle button on top of the list). Wait until all the the little cercles behind all the lines do not move anymore. Close U-block.
Good luck !