Is this all of the time, sometimes . . . . .

Start Firefox in Safe Mode {web link}

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

Every field in every website does the same thing. Opening in safe mode was a good suggestion, but didn't work. I have disabled all of the plugins and extensions, get the same problem. If I open word, type my response in word, I can copy and then paste into the Firefox opened dialog box with no problems. Problem does not occur with Chrome or Edge, neither of which I particularly like.

So the problem is only with Firefox, and Safe Mode does not help.

What's your computer system and Firefox version?

https://support.mozilla.org/en-US/kb/update-firefox-latest-version?cache=no Did you update Firefox to the latest version 66.0.1 March 22, 2019

Uninstalled Firefox, downloaded 66.0.1 and installed it. Same problem. I am running Win 10 home, rev 17763 on an IBuypower gaming computer.

I doubt this will help, but

Start your Computer in safe mode with network support. Then start Firefox. Try Secure websites. Is the problem still there?

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode Starting Any Computer In Safe Mode; Free Online Encyclopedia