So I guess I don't need to say this, but, don't call that number.

There are a few common patterns to these annoying "tech support scam" pages, and these are some techniques for closing them without having to take drastic measures:

(1) Large alert dialog (lots of text)

If you cancel this dialog, it may reappear. After two or three appearances, Firefox should add a checkbox at the bottom of the dialog to stop the site from showing more alerts. Check that box and click OK to block further dialogs.

(2) Authentication dialog (asks for username and password)

If you cancel this dialog, the page may reload and immediately show it again. Pressing the Esc key numerous times in a row can cancel the reload as well as the dialog.

(3) Reacting to mouse movement

Some pages have a script that detects when you are moving the mouse pointer up toward the tab bar and takes action to show another dialog to moves to full screen view to hide the toolbar area. On these pages, try using the keyboard shortcut Ctrl+w to close the tab instead of the mouse. (On Mac, Command+w)

Hopefully this will let you close problem pages without having to "kill" Firefox in the Windows Task Manager. (I don't recommend using that method because the tab will come back during automatic crash recovery anyway.)

Often these scam pages are promoted through ad networks. As a defensive measure, you could consider using an add-on that is effective at blocking ads, such as:

https://addons.mozilla.org/firefox/addon/ublock-origin/

As with any content blocker, this will cause problems on some sites, so keep an eye on its toolbar button in case you need to make an exception to get a page to load properly.

Just in case you got an unofficial Firefox install with some unwanted extras, here are some steps to take to check/clean your system:

(1) Open the Windows Control Panel, Uninstall a Program.

After the list loads, click the "Installed on" column heading to group the infections, I mean, additions, by date. This can help in smoking out undisclosed bundle items that snuck in with some software you agreed to install. Be suspicious of everything you do not recognize/remember, as malware often uses important or innocent sounding names to discourage you from removing it.

Take out as much trash as possible here. If you're not sure, feel free to post program names or a screenshot of the list.

(2) Since the Uninstall a Program list isn't necessarily complete, you can search for remaining issues with the scanning/cleaning tools listed in this support article: Troubleshoot Firefox issues caused by malware. These on-demand scanners are free and take considerable time to run. If they finish quickly and especially if they require payment, you may have a serious infection. I suggest the specialized forums listed in the article in that case.

(3) Finally, in Firefox, open Firefox's Add-ons page using either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• in the Windows "Run" dialog, type or paste
  firefox.exe "about:addons"

In the left column, click Extensions. Then, if in doubt, disable (or Remove, if possible) unrecognized and unwanted extensions. All extensions are optional; the troublemaker might not be obvious from its name.

Hopefully that will flush anything on your system and in your Firefox that could be a problem. If you want to run a fresh installer, you can get it from the following page (scroll down to your preferred language):

https://www.mozilla.org/firefox/all/