This is not an issue in Firefox 23.0.1. The pinned tab should only contain a logo of the current tab.

This could be a new feature in the up-and-coming Firefox versions.

Try downloading Firefox 23.0.1.

This could also be an add-on causing this issue.

Try Firefox Safe Mode to see if the problem goes away. Safe Mode is a troubleshooting mode, which disables most add-ons.

(If you're not using it, switch to the Default theme.)

• You can open Firefox 4.0+ in Safe Mode by holding the Shift key when you open the Firefox desktop or Start menu shortcut.
• Or open the Help menu and click on the Restart with Add-ons Disabled... menu item while Firefox is running.

Once you get the pop-up, just select "'Start in Safe Mode"

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, and you need to figure out which one. Please follow the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article for that.

To exit the Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

Please report back soon.

Thanks Computer Whiz, I have traced it to a theme add-on that must have updated itself. Now that I know the problem, I am now contacting the theme author to solve the issue.

What is the name of the theme?
Did you download the theme from Mozilla or another source?

Such close button is a bad idea and is very unlikely to be actually in Firefox.

ComputerWhizz, the theme was "FT DeepDark 8.1.1"

Waka_Flocka_Flame, totally agree and it isn't in firefox at all, the theme I was using must have put those buttons in so until the theme author changes it I am now using LavaFox V2-Blue instead which I am very happy with. :)

I saw that ComputerWhiz posted on AMO website a misleading review about my theme FT Deepdark. Before writing such reviews he/she should first check by him/herself if the problem was still there with the latest version of my theme, i.e. the 8.3. I made already 2 updates today even before he/she posted his/her negative comment calling users to uninstall my work. The pinned tab close button issue was a bug and not a wanted feature. Next time he/she wants to write a bad review first he/she should try to be sure of what he/she is telling...

Thanks for solving the problem sr21, for the record I actually checked at the time I created this thread that there was a new version and there wasn't one that was compatible with the version of the firefox browser I was using then the bug appeared.

I very much like your theme and will probably download the updated version when I get round to it and I would generally recommend it for others to use as well.

The problem is the negative review on my add-on's page that "ComputerWhiz" wrote. He/she wrote that review after I already made 2 updates which were solving the bug (it was a bug and NOT a new feature as some people stated without knowing). So actually he/she wrote that review when the bug was already fixed. He/she rated my work low and called users to uninstall it on my own add-on's page. I m sorry but I can t accept those kind of things. I ve been working on this add-on more than 3 years now and put a lot of my energy and freetime to create something nice that I would enjoy and that also Firefox's users could enjoy to use. And when I see such comments about my work, it really disturbs me. It s a lack of respect

I actually like your theme myself, though I manually update my addons, so I avoided this problem, but I my self appericate your work, espically where you can use a windows looking and sleek style to match my GTK theme.

EDIT: PS never wrote a reviews on AMO, maybe I should start appericating addon and theme devs.