Sounds like a keyboard issue.

Hello p31woman,

It could be that you accidentally turned on caret browsing : You turn it on by pressing the F7 key on your keyboard, but you will also have to turn it off by pressing the F7 key (you'll see a litte dropdown appear).

If that is the case (caret browsing being the culprit); here's what you could do (only if you want to avoid this in future) :

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

Type in the search bar :

accessibility.browsewithcaret

and :

accessilibility.browsewithcaret_shortcut.enabled

Make sure both values are set to false.

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

Any good  ?

Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Safe Mode start window

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems
• https://support.mozilla.org/en-US/kb/upgrade-graphics-drivers-use-hardware-acceleration