One that I could not live without was BBCodeXtra, which provided a context menu which allowed various tags in bbCode, vBulletin, Markdown, and HTML to be automated, along with users to create custom tags.
Right now, it is largely a copy of the menu structure of BBCodeXtra.
(on edit) I now have the program up on the releases page at gitHub.
As soon as this is on addons.mozilla.org, I will post the link to that here.
I have not formally put it in the Mozilla Addons, because it is still at a preliminary state, basically alpha.
The code is released under an MIT open source license, and you can find the source code on Github as bbCodeWebEx.
The icons are NOT under the MIT License, having been done by by Charles Saroff, and he holds the copyright under a yet as to be determined license.
While this will work with pre-Quantum (Firefox 56 and earlier) versions of the browser, the clipboard functionality does not work.