Make Zombiekeys compatible with Thunderbird 78

[RealRaven2000]

The main mechanism of getting the key listener to work with the UI are XBL bindings - these need to obviously be replaced.

Within Composer it would interesting to run the code from a content script - John Bieling gave a minimal example - see attached zip file.
_contentScripts.zip

[ovari]

@jobisoft can you please provide more help with porting Zombie Keys (Multilanguage Keyboard) to Thunderbird 78? Thank you

[eagerm]

I'll take a look at the code to see if there is anything I can help with.
-- Michael Eager (eager@eagercon.com)