[Idea] ThunderMonkey: GreaseMonkey for Thunderbird

I thought it would be nice to have an extension like Greasemonkey for Thunderbird.

That is: allow to write and share little javascript snippets that make certain changes in the appearance of incoming email.

You can already do that using proper extensions, but it is a little overkill, especially for beginners. So for the same reason that user scripts are popular despite having proper browser extensions.

I'm preparing a mockup of the interface. It could be similar to Greasemonkey, have a script manager, and an embedded editor.

The script manager:

The script editor window:

The main difference with Greasemonkey is that now we cannot match against an URL, but instead we have to match against email headers.

The scripts should also be able somehow to access all mail headers and body to do additional filtering.

Btw, I'm already used to writing user scripts, but not extensions.
Any thoughts or help is welcome :)