I have also run Firefox in Safe Mode, and the tabs are still opening themselves instead of staying in the background.

The GoodSearch toolbar can cause this issue. See /tiki-view_forum_thread.php?forumId=1...

You can try "Reset all user preferences to Firefox defaults" on the Safe mode start window - See http://kb.mozillazine.org/Resetting_preferences --- Create a new profile as a test to check if your current profile is causing the problems. See [[Basic Troubleshooting|#Make_a_new_profile|Basic Troubleshooting:Make a new profile]]

There may be extensions installed by default in a new profile, so check that in "Tools > Add-ons > Extensions".

If that new profile works then you can transfer some files from the old profile to that new profile (be careful not to copy corrupted files). See http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

I uninstalled the GoodSearch bar and restarted FireFox, the tabs are now opening in the background.

Thanks!

You're welcome

I didn't see an answer here that suited my situation, so I went looking in about:config from the url bar.

I found that changing the value from False to True on the following line worked for me;

browser.tabs.loadDivertedInBackground;true

Type about:config in the url bar, then in Filter area at the top paste in;

browser.tabs.loadDivertedInBackground

then right-click and click Toggle until it gets bold letters and/or says true at the end as in the above line.

Hope this works for you :-)