# Firefox 4 hangs during tab switching for several seconds

If you are experiencing problems with a hanging Firefox 4 after update to version 4.0.1 during tab switching, this line in your prefs.js (usually located at C:\Users\Username\AppData\Roaming\Mozilla\Firefox\Profiles\ProfileName in Windows 7) could be the reason:
user_pref("browser.taskbar.previews.enable", true);

Close your Firefox, remove the line out of prefs.js, save the changes and start Firefox again. Now the problem should be gone.