Get rid of what? You have not told us what the problem is.

What tabs? What site? What is in the tabs? . . . . . .

Hello,

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Thank you!

hello, what you've described is certainly not a part of firefox but it may be something that is caused by adware/malware that is active on your system. so please perform all these steps:

1. reset firefox (this will keep your bookmarks and passwords)
2. afterwards go to the firefox menu ≡ > addons > extensions and in case there are still extensions listed there, disable them.
3. finally run a full scan of your system with different security tools like the free version of malwarebytes and adwcleaner to make sure that adware isn't present in other places of your system as well.

Troubleshoot Firefox issues caused by malware

Your Question Details > More System Details shows a suspicious extension named "DiscountSmasher" that may be generated unwanted ads and tabs.

Here's my suggested procedure for tracking down and cleaning up unwanted add-ons. I know it seems long, but it's not that bad.

(A) 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.

(B) Open Firefox's Add-ons page using either:

• Ctrl+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 Plugins. Set nonessential and unrecognized plugins to "Never Activate".

In the left column, click Extensions. Then, if in doubt, disable (or Remove, if possible) unrecognized and unwanted extensions. Bear in mind that all extensions are optional, none come with Firefox.

Often a link will appear above at least one disabled extension to restart Firefox. You can complete your work on the tab and click one of the links as the last step.

Any improvement?

If you have some additional time:

(C) You can search for remaining issues with the scanning/cleaning tools listed in our 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.

Success?

P.S. The current version of Firefox is 39.0.

Fred, look at the title.

When I close a web site, I get the pop up that says "you're about to close two tabs. Do you want to continue?"

I only have one "tab" open. But I have to take three steps to close it.

I'm not the first to have this problem.

Thanks for the additional detail. This can occur when an add-on opens a hidden tab in a different tab group. When you see that message next time, cancel the close and check for a second tab group. You can press Ctrl+Shift+e to open/close the tab group screen. Can you find the second tab there in a different group? If so, what is the URL? That might be a clue to the culprit.

The solution was simple. I had the "warn me" in the popup window checked. I unchecked it. The problem went away. No reprogramming, etc.

You had Firefox warn you when closing the window would close multiple tabs, but you said there weren't multiple tabs in the window so the message should not have appeared. Still seems suspicious to me.