Try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes).

If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:

• Click the menu button , click Help and select Restart with Add-ons Disabled.

If Firefox is not running, you can start Firefox in Safe Mode as follows:

• On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.
• On Mac: Hold the option key while starting Firefox.
• On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode
  (you may need to specify the Firefox installation path e.g. /usr/lib/firefox)

When the Firefox Safe Mode window appears, select "Start in Safe Mode".

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, theme, or hardware acceleration. Please follow the steps in the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.

To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

This does work…thank you so much. Why did this happen all of a sudden? I lost many bookmarks. And this issue of hypertext links not working also just occurred. I will see if safe mode fixes hypertext links….can I just stay in safe mode all the time?

Hypertext links seem to work now!!! This is so weird. I've used this browser for years with never any problem. Did something bet contaminated?

SafeMode is a troubleshooting mode. After using the SafeMode and then returning to 'normal mode' if your problem is solved chalk it up to luck. Most of the time further diagnosis is needed.

https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems