You need to give steps on what you did that this happened. Also firefox isn't a email program but just a Browser so you need to check with the online email server you using to make sure the settings are correctly set for thunderbird to work.

I gave the exact process: two clicks. I know that FF is not an email program, of course, but it has the function to send a link in that menu. If TB is not running, it works. If TB is running, the error message is obtained. TB works. This has nothing to do with a server, it is entirely to do with the either the way that the FF call is made or the way that TB handles it. It has been denied that it is a TB problem and I was directed here. It is a bug. Perhaps I should post it as such. Other programs do the job properly (Acrobat, Acrobat Reader, ThumbsPlus), why not FF?

If it is a bug then you need to use the bugzilla to report the issue if is a bug related problem.

As I thought, but just following the advice given ...