Browser Addons: FF,Chrome,Safari,IE

my project is just a simple script that i want to add to all websites that a user opens. Just like [login to view URL] sidebar or any bookmarklet works, but instead of clicking the bookmarklet, i want the script to be automatically added to the page. There will also be a small button in the sidebar that will light ON when it's active, and a user can click it OFF so that it stops adding the script to pages. It is a very simple concept. The proposing freelancer must have experience with browser plugins and some understanding of how bookmarklets work. I already have all the script code ready that will be added to pages..i just want the addons that will insert this script into the html document of every website a user visits. Addons needed are for: Firefox, Google Chrome, Safari, and Internet Explorer