developing browser extension for content filtering

I'm developing an application for content filtering. i'll use it as web service but my problem is that i hadn't developed any extension for firefox or ie before. i read some about firefox extensions and now i know a little about it.

firstly can i use web service in a firefox/ie extension? if yes, can you give me a link of tutorial or sth like that?

all sugg开发者_开发知识库estions are welcome.

The question is too broad. Yes, you can call a web service using XMLHttpRequest, for example.