First you have to create a signature (html or text - no file signaure!), if you would like to have no signature as default then choose 'add signature from file' and leave the filename empty! Now no signature is added by default and you have the option to add the signature by right-clicking. Just click the right mouse button in a new e-mail and insert the signature. Therefore, I have crafted this little add-on which adds this function. The afterward addition of signatures in e-mail is apparently not provided, the functionality can not be found anywhere. I'm tired of all this, and as i have another real job to afford my bills, i'm not ready to make all that effort for so few consideration. I have had already several bad experiences in the past when my addons got broken just because Mozilla changed something which used to work without even thinking about compatibility or giving information. That is not the first time that Mozilla is acting as if addons developers and the community was not important. I mean a relevant guide, not an information note explaining that the addons should be restartless, turned into webextensions and so on, and not even giving an example. If you have multiple email accounts, you must configure signatures separately for each account. Click Tools Edit > Account Settings, and then, in the left panel, select the account for which you want to create a signature. Besides the fact Mozilla leaves us doing the 'dirty work', they are not even able to provide detailed information about how to make the old addons compatible with their new standards. Signatures are created in Thunderbirds Account Settings interface. TB v68 compatibility note: There is no plan to move the addon to the TB v68 'standards', and here is why: - Mozilla itself has decided not to work on compatibility developments and leave 'that' to the addon developers.

Mozilla thunderbird signature