Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

See:

• http://kb.mozillazine.org/browser.link.open_newwindow
• 1: current tab; 2:new window; 3:new tab;

For links opened via JavaScript you can look at this pref:

• http://kb.mozillazine.org/browser.link.open_newwindow.restriction

I assume this doesn't happen with every link, but only particular ones/kinds/sites. If you notice a pattern to the problem, could you describe the problem in more detail?

I cannot believe that anyone would prefer a new tab over opening a new window.

All too often I am destroying work and recordings when I accidentally click to close a window and shut down several operations. Personally, I would prefer either a double click to close a window or a two step operation to do so.

Now that I see some instruction on how to put this back to what it used to be (win XP?) I will probably not frighten my cat so much when I break out using my Microsoft Vocabulary.