What Files are you trying to open? Are these files on your computer, a website, your email, etc? Can you just give a bit of background on what your issue is and how it affects Firefox's operation on your PC?

Hello,

thanks for answering and trying to solve my problem. The files are in my email system Mozilla Thunderbird and thus are emails which I have stored in various files. Some file I can open and others produce the message I had sent.

Thanks again

Lutz

For thunderbird support, please go to http://support.mozillamessaging.com/en-US/home and the community thee can assist you.