How to write an extension for Firefox?

Question

Mozilla Firefox

Hello!
There is a task, you need to write an extension for FF for a specific site that will work with html strings (replace, attach, change styles, and so on).
I am a complete layman in plugin building, besides, I know English very poorly, in Russian the manuals that I have seen are very scarce and it is not so easy to understand what and how to do.
I ask for specific help, please tell me what file structure and what files are needed for my task. How exactly to make the plugin cling to a specific site. I read that some kind of overlay is needed, but I still don’t understand what it is, whether it is needed for my task and how to work with it. It is desirable that all the necessary operations could be done using JQuery (the question is how to connect it).
Perhaps, out of ignorance, I didn’t ask for some nuance, I will be glad if you also point it out and explain how to do it ... Thank you

Answer 1

I advise this site - xbb.uz/XULRunner/Getting_started_with_XULRunner.html
Making extensions for FF is easy. Mozilla has manuals in Russian.