hello clarissaz, this sounds like a problem that could be caused by malware. please go to tools > addons > extensions & remove any suspicious entries (toolbars, things that you have not installed intentionally, don't know what purpose they serve, etc).

Remove a toolbar that has taken over your Firefox search or home page Troubleshoot Firefox issues caused by malware

as an alternative you could also try to reset firefox...

See also [/questions/946173]

I also have this problem, very annoying. Clearing cookies, cache, etc doesn't work and I have no new add-ons, only have very few that I need, nothing that causes problems. Tried looking up about it and it seems to be caused by certain sites at times I guess but I can't find a good fix. I don't have anything with spam emails though, just this window popping up.

Did you try Safe mode?

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

I cleared the cache and cookies, nothing happened yet today, so cross fingers this took care of it. Also, I ran a scan with norton, and hopefully that took care of any malware trying to do evil on my computer!

Macs don't have a safe mode

Mac do have a Firefox Safe mode that you can enter if you hold down the Options key while starting Firefox.

You can use one of these to start Firefox in Safe mode:

• On Windows, hold down the Shift key while starting Firefox with a double-click on the Firefox desktop shortcut
• On Mac, hold down the Options key while starting Firefox
• Help > Restart with Add-ons Disabled

• https://support.mozilla.org/kb/Safe+Mode