• "Clear the Cache": Tools > Options > Advanced > Network > Offline Storage (Cache): "Clear Now"
• "Remove the Cookies" from sites that cause problems: Tools > Options > Privacy > Cookies: "Show Cookies"

I've tried all of the above and I still have the problem

It is possible that there is a problem with the files sessionstore.js and sessionstore.bak in the Firefox Profile Folder.

Delete the files sessionstore.js and sessionstore.bak in the Firefox Profile Folder.

• Help > Troubleshooting Information > Profile Directory: Open Containing Folder
• http://kb.mozillazine.org/Profile_folder_-_Firefox
• http://kb.mozillazine.org/sessionstore.js

If you see files sessionstore-##.js with a number in the left part of the name like sessionstore-1.js then delete those as well.
Deleting sessionstore.js will cause App Tabs and Tab Groups to get lost, so you will have to create them again (make a note).

See:

• http://kb.mozillazine.org/Session_Restore

I had this problem. Open Firefox, go to tools, go to options, go to tabs....check the box beside....When I open a new tab switch to it immediately......this worked for me.

I have tried all of the above none work for me.