Creating extensions / addons

I am interested in creating browser addons / extensions.
Has anyone here done this before and can you share your experiences? How did you find it?

If you know HTML/CSS/JS then you can create an extension easily, as that's all you need. Then go on Chrome's developer site and look for the general guides to get started. It's not hard, the hard thing is coming up with a good extension to create

I did it for Mozilla Firefox.
You should know js/css/html.

I used guide by mozilla (click)