When you hover your mouse pointer over the tab in the tab bar, Firefox behaves as though you took one of the two actions that moves the tab to a separate window? Those are:

• click and drag down to "tear" the tab off the bar
• right-click or Ctrl+click the tab > Move to New Window

Or do you mean this happens when hovering the mouse pointer over the page in the tab?

Either way, hovering shouldn't do anything, but maybe someone will get a clearer idea of what might be going on.

Meanwhile, Could you test in Firefox's Safe Mode? That's a standard diagnostic tool to deactivate extensions and some advanced features of Firefox. More info: Diagnose Firefox issues using Troubleshoot Mode.

If Firefox is not running: Hold down the Shift (Mac: option) key when starting Firefox.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement?

Regarding the address bar, sometimes called the location bar, when does the cursor move there?

• immediately after the page loads?
• when you start typing in a form field?
• other?

There are a number of keyboard shortcuts that could move the cursor to the location bar, including: F6 and Ctrl+L (Mac: Command+L). Not sure whether Firefox might be confused about the status of your Ctrl/Command key. In that case, it sometimes helps to press and release it several times.

I don't use any keyboard shortcuts. I checked my mouse settings and it had been re-set to use smart move. Don't know how, but been using pc long enough to know that sometimes things just re-set on their own. I unchecked it and it's fine now. thanks