A single quote mark ' or a slash / will activate Quick Find from the keyboard, when the "focus" in on the webpage. https://support.mozilla.org/en-US/kb/search-contents-current-page-text-or-links#w_quick-find

Not sure there's a way to disable that feature, but if the cursor is in a text area on a webpage or in the URL bar Quick Find won't open.

That's not what's engaging the "find". Any typing in any text box will randomly shift to find. At times find won't release the cursor or close and I have to reboot Firefox (and sometimes that won't do it). If I don't realize right away that find has taken over and hit enter the computer will go into an endless find loop which sometimes requires rebooting the entire system after killing Firefox in Task Manager.

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.

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.

Nope - safe mode doesn't help