Thunderbird (with Firefox) problem with links not working in emails

I’m delighted with Firefox and Thunderbird, but suddenly for some unknown reason, when I get an email with a link (in blue), clicking it results in…nothing. This did not happen before. In Hotmail or Yahoo, it worked all right until today, when that stopped too.

Wassup? I posted on the TB forum and nobody had any idea, but one person wrote they had the same problem.

Any ideas?