This sounds like it may be caused by an extension.

Try the Firefox Safe Mode to see how it works there. The 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 the Firefox 4.0+ Safe Mode by holding the Shift key when you use the Firefox desktop or Start menu shortcut.
• Or use the Help menu item and click on the Restart with Add-ons Disabled... menu item while Firefox is running.

Don't select anything right now, just use "Continue in Safe Mode." To exit the Firefox Safe Mode, just close Firefox and wait a few seconds before using the Firefox shortcut (without the Shift key) to open it again.

See if you can reproduce the problem in Safe mode, if not, this is an extension problem. You can use the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to fix it.

When you figure out what is causing your issues, please let us know. It might help other users who have the same problem.

Start Firefox in Safe Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance/Themes).

• Don't click the Reset button on the Safe mode start window or otherwise make changes.
• https://support.mozilla.org/kb/Safe+Mode

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

do you use the extension "dragdropupload"?

https://addons.mozilla.org/de/firefox/addon/dragdropupload/

Disable this extension.

D Funny... Just got this error -> Image

Disabled dragdropupload 1.9.38 and... Hellaluja! so far so good...

One final question: Does FF automatic update checker look for updates on disabled add-ons?