Can't open web link from Mail

I hope someone out there can help: for the last few days I suddenly haven't been able to access the web link to my default browser (Firefox) from an email via Mac's Mail. I've not changed any settings anywhere, I've checked out all the obvious ones, and it has always worked fine before, just by clicking on the link in the email. I haven't installed any updates or new software recently. I looked on the support pages of Apple Mac's website and apparently a lot of people are having the same problem (and not just with Firefox), but no-one seems to be able to come up with a solution.
Yes, I suppose I could get round it by copying and pasting; but that's annoying after you've been used to it happening all by itself; and you don't always get the link, you just get 'click here.'
Has anyone else had the same problem, and if so how have you resolved it?
With many thanks for any help

Hold "ctrl" or  while clicking? I've not had the problem, but I know that with some text editors this is what I have to do to get the link to open.

Thanks very much for this, Moss - it worked! - or something did! You know how it goes - lots of 'Maybe if I try this' and afterwards you can't remember what you did? But even if it wasn't the solution you suggested, it's still a very useful tip.

Glad to hear that whatever you did fixed it!