1. First remove the Google+Facebook app from your Facebook Profile for that
Login to your Facebook account>from Account drop down menu select “Privacy Settings” and click “Edit your Settings” under “App and Websites”, for Google+Facebook app click “Remove App” link.
2. Delete Google+Facebook extension if installed in Chrome browser.
3. Delete Google+Facebook extension in Firefox also. Restart your browser.
Now type about:config in the address bar and proceed by agreeing to the warning. For the below entries right-click on each entry and click “Reset” button to restore its default values.
Restart your Firefox browser.
Read more details about Google+Facebook suspicious behavior here.
You can use ecleaner add-on for Firefox to check and remove preferences saved by this extension after its uninstallation.