Do you use any add-ons related to popups?

Could you test in Firefox's Safe Mode? In its Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, and some other advanced features to help you assess whether these are causing the problem.

If Firefox is not running: Hold down the Shift 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?

Eureka and viola! It appears the pop-up blocker is the problem. I have also been having issues with AVG and, come to think of it, those appeared at the same time. I will work on this more later today. Probably start by getting rid of the pop-up blocker. I already dumped AVG (yesterday) due to pop-ups trying to get me to renew paid coverage - that I don't remember ever having.

Thank you so much for the accurate and easy to implement solution. Kudos!

Hi capn27, to make the thread a complete reference, I'll add this:

You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions.

Then cast a critical eye over the list on the right side. Any extensions Firefox installs for built-in features are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. Anything that could block the desired content? Anything suspicious or that you just do not remember installing or why? If in doubt, disable (or remove).