I would not call that number.

When you crash Firefox using End Process in the Task Manager, usually Firefox will try to restore the last windows and tabs you had open, so that could explain why you see that message again.

If you are not using End Process, this could be a bad add-on or a one-time session restore.

To try to bypass that, after you "kill" Firefox in the Task Manager, try pasting the following in the Windows start menu search box and pressing Enter to run it:

firefox.exe -safe-mode "about:sessionrestore"

Hopefully that will launch a list of windows and tabs with the option to restore selectively or to start a new session. Safe Mode deactivates extensions. Does that get you to a usable state?

. Whenever you get a message / popup like that;

DO NOT USE ANY OF THE PROVIDED LINKS OR ANY PHONE NUMBERS ! !

Such messages are only Spam that could lead you to Fake Support. Not only can they damage or hack your system, they charge you to do so.

You can report such a site at; Google Report Phishing Page {web link} which is the same when done while on site by going to Help > Report Web Forgery

Help us safeguard Mozilla’s trademarks by reporting misuse {web link}