Hi, If you are referring to Tiny Menu, it is no longer maintained, so may be causing your problem. Can you try disabling it? Ctrl + Shift + A > Extensions.

Alternatively you could try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes).

If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:

• Click the menu button , click Help and select Restart with Add-ons Disabled.

If Firefox is not running, you can start Firefox in Safe Mode as follows:

• On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.
• On Mac: Hold the option key while starting Firefox.
• On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode
  (you may need to specify the Firefox installation path e.g. /usr/lib/firefox)

When the Firefox Safe Mode window appears, select "Start in Safe Mode".

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, theme, or hardware acceleration. Please follow the steps in the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.

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

When you figure out what's causing your issues, please let us know. It might help others with the same problem.

Hi again, Nope, this didn't solve it. I'm running Compact Menu 2, not Tiny Menu. My partner has the "+" on his computer, which is why I suddenly realized I was missing it. I have, however, found a wee "add tab" button that I added to that bar, dragged it to the far left (the only place other than far right that it would go), and this is working well. So if we don't resolve the "+", I'm OK. I appreciate your prompt reply, Scribe....

...forgot to mention--my partner has all the same bars and settings as I do, so it seems weird we have this one difference.

The new tab button can be dragged to another toolbar and then it becomes a new tab toolbar button with its own icon.

You can click Restore Defaults in the Customize palette window to restore the plus icon on the Tab bar to its default position.

Thanks Cor-el, I was trying to avoid the restore default option, since I have a very customized set of bars--however, that did the trick, and I'm now trying to remember what I had where. I never thought to do a screen shot first....

There is an Undo button after you have clicked Restore Defaults, so if you have this button then you can reverse the process and make a note.

The current customization is stored in the browser.uiCustomization.state pref in JSON format. You can paste this JSON content in the Scratchpad (Firefox/Tools > Web Developer). Click the "Pretty Print" button to format the content for readability.

You can open the about:config page via the location/address bar. You can accept the warning and click "I'll be careful" to continue.

• http://kb.mozillazine.org/about:config