Now two of my extensions are also available in FireFox – JIRA Issue Opener and URL With Parameter Opener.
Making extensions for FireFox is harder than making them for Chrome. Documentation and tutorials are tricky and the structure of files is more complicated. So writing hello-world extension for FF took me a long time.
But there is one thing, that is more convenient in FF than in Chrome – using properties/preferences/options. In Chrome you should create your own HTML page for that (in FF you can just list properties and they will appear in the standard addon's settings window). And for getting options in Chrome you should use asynchronous functions (which makes you to write ugly code) – in FF options are basically stored in array and it's really easy to get and set them.