i had this on one of my laptops. There was an addon called "browser highlighter" or something close to that. I removed that addon and the problem stopped.

Thanks for your help, nobaudee. Your solution is correct. I actually identified and fixed the problem three weeks ago. I think the "browser highlighter" is craplet that gets added when you use skype or several other programs. For anybody else that has this same problem, just uninstall "the browser highlighter" via the add/remove option within control panels. It's a simple for a nagging problem.

If you want don't like blindly using advice from a forum, then google "troubleshooting extensions and themes for Firefox. Follow the sections titled "Disable all extensions" and "Test for faulty extensions".

The following is a copy of the two sections listed above:

Disable all extensions

To determine whether a faulty extension is causing your problem, you can disable all of your installed extensions:

  1.

     At the top of the Firefox window, click on the Firefox button (Tools menu in Windows XP), and then click Add-onsOn the menu bar, click on the Tools menu, and then click Add-onsAt the top of the Firefox window, click on the Tools menu, and then click Add-ons. The Add-ons Manager tab will openAt the top of the Firefox window, click on the Tools menu, and select Add-onsOn the menu bar, click on the Tools menu, and select Add-onsAt the top of the Firefox window, click on the Tools menu, and select Add-ons. The Add-ons window will open.
  2. In the Add-ons Manager tabwindow, select the Extensions panel.
  3. Click the name of an extension in the list to select it.
  4. Click Disable to disable the selected extension.
  5. Repeat this for each of the other extensions in the list.
  6. Click Restart Firefox. 

After you restart Firefox, all extensions will be disabled. Test for your problem.

   * If the problem still occurs with all extensions disabled, it is most likely that the localstore.rdf file in your Firefox profile is corrupt. You can Reset toolbars and controls to resolve the problem. 

If the problem no longer occurs with all extensions disabled, one of your extensions was causing it. To find the extension that was causing your problem, continue as follows:

test for faulty extensions

To determine which of your disabled extensions was causing your problem, you can re-enable each extension one at a time.

  1.

     At the top of the Firefox window, click on the Firefox button (Tools menu in Windows XP), and then click Add-onsOn the menu bar, click on the Tools menu, and then click Add-onsAt the top of the Firefox window, click on the Tools menu, and then click Add-ons. The Add-ons Manager tab will openAt the top of the Firefox window, click on the Tools menu, and select Add-onsOn the menu bar, click on the Tools menu, and select Add-onsAt the top of the Firefox window, click on the Tools menu, and select Add-ons. The Add-ons window will open.
  2. In the Add-ons Manager tabwindow, select the Extensions panel.
  3. Click the name of an extension in the list to select it.
  4. Click Enable to enable the selected extension.
  5. Click Restart Firefox. 

After you restart Firefox, test for your problem. If the problem comes back, the extension you just enabled was causing it. Note: If you have a large number of extensions, it may be quicker to enable more than one extension at a time. The method with the fewest number of restarts required is: Enable half the extensions in this list, then restart Firefox and test for the problem. If the problem reoccurs, you know that the faulty extension is one of the ones you just enabled. If the problem does not occur, you know the faulty extension is one of the disabled ones. Repeat the process until the faulty extension is found.

After you find the extension that was causing your problem, disable or uninstall the faulty extension and re-enable the other extensions in the Add-ons window.