I'm new to thunderbird addon development but I want to create something
that should be relatively simple.
I'd like to create a new chat message style (Preferences > Chat >
Message Styles). The available styles don't work particularly well for
IRC so I'd like to create a tweaked version of the existing Simple theme
(the font wrapping means it's difficult to read longer lines).
I've found the relevant CSS in comm/im/themes/messages.
I have the following questions:
1) What is the relevant API call to register a new theme so it appears
on the list and can I do this from an addon?
2) Do I need to copy/paste the simple theme's directory and provide my
tweaks or can I inherit from it and just provide the 10-15 lines of CSS
I want to change?