FC7 and Thunderbird

[Tim and Alison Bentley]

I have installed FC7 over the top of FC6 with no problems apart from the
upgrade to Thunderbird.
I am now unable to click on a URL within a email and open Firefox.
Under FC6 this worked fine but under FC7 all I get is a box with ERROR
in the heading.
I have tried to reinstall Thunderbird but this has not worked.

Has anyone any ideas so I am able to use Thunderbird.

Thanks

Tim