This is a "completed" version of this add-on, by which I mean I implemented everything* I originally wanted to add to this project (see backstory in README for details). I also refurbished the code for quite a bit, as the original one was quite a mess written in a hassle :)

Changes:

• Added dataset import/export
• Implemented autosave system (uses localStorage)
• Added class removal mode (allows to remove classes you don't need anymore)
• Some terminology fixes
• Performance improvements, code cleanup and separation

P.s. the .XPI below is not signed, meaning you can only install it as temporary add-on!
To install signed version, check https://addons.mozilla.org/ru/firefox/addon/drawachar/