As a derivative (also affects plugins) of hexchat, this project has to be GPLv2-compatible. (the MPL isn't)
SpiderMonkey, as part of Firefox, is afaik under multiple licenses MPL/GPL/LGPL, therefore a license change shouldn't be problematic.
**GPLv2+** would be nice
good project ;)
I'm no expert but everything I've read on it says it is compatible: https://en.wikipedia.org/wiki/Mozilla_Public_License#Compatibility_with_other_licenses
If you have any other sources that state otherwise I may be interested.
Also how is a plugin derivative?
The stuff i read, must have been about the old MPL 1.1,
MPL 2.0 is GPL-compatible, sorry for my mistake.
add. infos about plugins and GPL (FSF):
http://www.gnu.org/licenses/gpl-faq.html#GPLAndPlugins