Any chance you inadvertently set your Firefox homepage in two separate tabs? The pipe symbol is used to separate homepage page settings.

http://tab-one.com|http://tab-two.co.

http://support.mozilla.com/en-US/kb/How+to+set+the+home+page

The same problem just occurred when opening up your post. Two pages shown on the toolbar, both displaying the same post when opened.

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

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.com/kb/Safe+Mode

• Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

In Firefox 4 you can use one of these to start in Safe mode:

• Help > Restart with Add-ons Disabled
• Hold down the Shift key while double clicking the Firefox desktop shortcut (Windows)

I didn't work, then it did. I'll wait and see over time. Thanks for the advice.