Try Firefox Safe Mode to see if the problem goes away. Safe Mode is a troubleshooting mode, which disables most add-ons.

(If you're not using it, switch to the Default theme.)

• You can open Firefox 4.0+ in Safe Mode by holding the Shift key when you open the Firefox desktop or Start menu shortcut.
• Or open the Help menu and click on the Restart with Add-ons Disabled... menu item while Firefox is running.

Once you get the pop-up, just select "'Start in Safe Mode"

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, and you need to figure out which one. Please follow the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article for that.

To exit the Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help other users who have the same problem.

I have the same problem as OP. I have tried safe mode but it doesn't solve the problem.

Very annoying! Why can't I just click an empty box in the new tab window and enter a URL? Why can't I drag a URL from another window?

It doesn't make sense to make adding a new page a multiple step (through the bookmarks window) process in the first place. But then it doesn't even work.

I had this problem when i had the box next to"Always use private browsing" ticked. When this is unchecked, problem solved. Whenever i need to drag a site to the new page tab, i need to disable private browsing, then turn it back on again. You may need to check the settings in "clear history when firefox closes"to make sure it does not delete the site preference.