Question: I'm to make a firefox extension which will inject some js code as well as whole jQuery lib.
I want it to happen (the injection) when user pushes the button placed somewhere in the browser. I have read docs form MDC and other tutorials about making the extensions and they seem complicated to me. Technologies such as XPCOM or XUL are completely useles form me (I have no time to learn them in fact). My question is, is it another way of solving my problem then following MDC? I need to find quicker way of doing my task. 
I've already written the extension for Google Chrome, and it was a way simplier than doing it for Firefox.

Answer: 
I would take a look at [Greasemonkey](http://www.greasespot.net/). It shares some similarity with Chrome plugins in function (Script gets injected on the page, local storage, etc). As for using JQuery with Greasemonkey, look at this question: [How can I use jQuery in Greasemonkey?](https://stackoverflow.com/questions/859024/how-can-i-use-jquery-in-greasemonkey)
You can use a [bookmarklet to add jQuery](http://www.learningjquery.com/2009/04/better-stronger-safer-jquerify-bookmarklet/) to a page and/or inject any other code.