hello, this is caused by the acceleratetab addon that you have installed. please go to the firefox menu ≡ > addons > extensions & disable or remoe it.

Now I have to figure out what installed this. Thanks.

I got this problem only when I updated to Firefox 32.

I can't find the place to disable as suggested in your reply. "addons > extensions & disable or remoe it"

Please help. Thanks

I don't have that add-on but I do have this problem. Any other ideas?

Try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that turns off some settings, disables most add-ons (extensions and themes).

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

• In Firefox 29.0 and above, click the menu button , click Help and select Restart with Add-ons Disabled.
• In previous Firefox versions, click on the Firefox button at the top left of the Firefox window and click on Help (or click on Help in the Menu bar, if you don't have a Firefox button) then click on 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, and you need to figure out which one. Please follow 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.

I uninstalled a whole bunch of add-ons & it works now, I'm sorry I can't tell you which one did the trick. I have no idea where/when most of them got installed! I left only the ones I recognised - if something doesn't work I'm sure I'll get a message telling me to re-install whatever's necessary. Many thanks.

I finally found the place to fix this problem as per the instructions given, I just wasn't looking in the right place. It's all OK now. Thanks, Di