Hi, delete all references to Yahoo, as shown under the heading 'How do I remove a single website from my history?' in this article - Delete browsing, search and download history on Firefox, then try the site (not from an old bookmark) again.

If that doesn't work, 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.

If still not fixed, please tell us the exact error message.

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

This fix did nothing to resolve the problem. Here's the exact error message I am getting when I try to attach files from my 'documents'.

Please check your internet connection We are unable to communicate with your inbox. You can also reload the page to try to reconnect. How do I fix my internet connection? I'm connected but still cannot access mail Error 18

What do I do next. I have to get this resolved ASAP.

Hi, if you have a 'Trusteer' program on your PC please try updating or disabling it.

If that doesn't help, it may be an issue with your AV which perhaps you could try temporarily disabling to test.

Yahoo has confirmed this was an issue server-side, and has pushed a fix to correct it. Uploads should work correctly now.