Quicktext is a Thunderbird extension, which has been created by Emil Hesslow. However, he was no longer able to update Quicktext or provide any kind of support. Thankfully he changed the license of Quicktext to MPL 2.0, so I could continue to update the extension and make it work with the most recent version of Thunderbird.
I will try to keep Quicktext going, but support will be limited. You may use the issue section of this repository to report bugs. You may also discuss Quicktext related issues with other users at https://discourse.mozilla.org/c/thunderbird.
Note: Emil maintained two versions of Quicktext, a free “Standard” version and a paid “Pro” version with additional features. Since he released both versions under MPL 2.0, the official version of Quicktext is based on the “Pro” version. However, the name of the extension remains just “Quicktext”. There is no longer a seperate Quicktext Pro version.
More information and usage descriptions can be found in the wiki of this repository.
The latest release and a change log can be found on addons.thunderbird.net.