Its coming due to google has been changed the login from
www.google.com/accounts
to
accounts.google.com
Solution: Open up toolbar.js with in some editor.
Find: www.google.com/accounts
and replace ALL with: accounts.google.com
Restart Firefox
Login through the toolbar.
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You can find toolbar.js file on below location.
->open run command
->go to %AppData%\ location
->search toolbar.js
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Have fun :)
