See Advanced JavaScript settings and disable Raise or lower windows.

Hope it helps.

Do you have that problem when running in the Firefox SafeMode?
A troubleshooting mode.
1.You can open the Firefox 4.0 SafeMode by holidng the Shft key when you use the Firefox desktop or Start menu shortcut.
2. Or use the Help menu item, click on Restart with Add-ons Disabled... while Firefox is running.
To exit the Firefox Safe Mode, just close Firefox and wait a few seconds before using the Firefox shortcut to open it again.

If not, see this:
http://support.mozilla.com/en-US/kb/troubleshooting+extensions+and+themes

Dear users. It is really annoying involuntary call from any site, including this "barisderin.com. I noticed this started happening after doing the installation of some add-on. "So I started to uninstall each add-in "individually to see which one this was related to the malfunction of Firefox. After disabling "Personas Rotator 1.2" which changes periodically personas skins, just the problem. So uninstall this add-on "and even deletes the listing

Can anyone help? I have the same problem. I am on a Mac OS 10.6.8 and I recently installed firefox plus some add-ons. When I launched Firefox I repeatedly got an extra tab to http://barisderin.com web page. I have removed the firefox folder from the library, removed the Firefox preference file from the preference folder in the library and also removed the application support folder for Firefox. In Firefox preferences I have removed the cookies to the website, blocked the website and checked the do not track me box in the preference. Nothing gets rid of the tab. I have uninstalled Firefox three times, each time going through the process mentioned above but I still get the tab though I have no add-ons or and I have not installed Personas.