Problem opening a new tab with Firefox

[Ukdodger]

Opening a new tab in Firefox (when a Firefox browser is already open) results in the message:- 'The address isn't valid. The URL is not valid and cannot be loaded'.

I've tried disabling all the add ons without result.

Any ideas. Thanks.

 

[UsernameIssues]

If this reset fails...
https://support.mozilla.org/en-US/kb/reset-firefox-easily-fix-most-problems

...try a new profile:
https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

 

[Not Myself]

Standard diagnostic - Firefox - MozillaZine Knowledge Base