Firefox Won't Open New Windows or Tabs – The Fix
To get to the bottom of this problem, the normal set of steps would be to disable all of your add-ons one by one, and remove each of your Firefox extensions one at a time to narrow down why Firefox won't open new windows and tabs to one particular extension or add-on.
Fortunately, however, several users have already gone through this, and we now know from experience that this fault is related to a Skype add-on, Microsoft .NET framework add-on or Java.
There is also a chance that other user-installed Firefox features are to blame, but as a general rule removing any or all of the above will get your browser working properly once again.
These extensions can be disabled via Tools > Add-ons > Extensions – simply select the one you want to remove and click Disable. Restart Firefox each time you do this to ensure the function has been disabled.
Ultimately, however, this may not resolve the issue; a reinstall of Firefox may be necessary.
Screenshot courtesy of author.