Smart P7M Support

"p7m" attachments are files with a digital signature that confirms sender's identity.
Since Thunderbird considers just the attachment type (content-type), it's more correct talk about attachments with type application/pkcs7-mime or application/x-pkcs7-mime.
Teorically Thunderbird should automatically verify signature and show attachments in postive case; if the verify fails, attachments are hidden.
Unfortunately this verify seems not work properly in some cases, even if you import new certificates.
Is this a Thunderbird bug or it depens from wrong settings? As far as I concern, I'm not able to give an answer and I don't know official documentation about this problem, except bug n243833.

While waiting an "officiale" answer from Thunderbird developers, this extension - build after lots of tests - can "unhide" and handle "p7m" attachments.

Note: to see the p7m attachments in print/print preview, you must use the extension PrintingTools - version 0.2.15 or higher.

Changelog 0.2.1 version:
- compatibility with Thunderbird versions for Debian and Ubuntu;
Changelog 0.2.2 version:
- added license text (GPL);
- works also with p7m attachments with type application/x-pkcs7-mime;
Changelog 0.3 version:
- new name;
- the extension now doesn't break anymore the Thunderbird capacity to decrypt crypted messages, when Thunderbird is able to do it;
Changelog 0.3.1 version:
- better code;
Changelog 0.4 version:
- new code that is faster and doesn't require never reloading message;
Changelog 0.4.1 version:
- the extension now can handle also messages without "Content-type" in headers;
Changelog 0.4.2 version:
- fixed compatibility with Enigmail + PGP;
Changelog 0.4.3 version:
- compatibility with Thunderbird 3.1;
Changelog 0.4.4 version:
- now it works also if it's installed globally;
- compatibility with Seamonkey 2.0 - 2.1 (not tested by me);
Changelog 0.4.5 version:
- compatibility with Thunderbird 5;
Changelog 0.4.6 version:
- compatibility with Thunderbird 9;
Changelog 0.4.7 version:
- compatibility with Seamonkey 2.2;

Download Smart P7m Support - 0.4.7 version (compatible TB 1.5-9 / SM 2.0-2.4)