Browser Add-ins/plugins

I require a plugin for windows itself whereby it will allow the feature to analyse and incoming web pages and modify the HTML. The purpose of this is to be able to display a html toolbar at the bottom of every web page the user loads. I want a browser independent way of doing this, which I have been told is possible. So it will work with all browsers. This area of prgramming is totally new to me so i'm going to need some serious dumbing down. lol. I want the plug-in to also be able to monitor the pages that have been visited, to be able to change the toolbar depending on the page the user is on. There are a few more features that I would like to discuss with any prospective and ablle prgrammers. Even just to say that this owuldn't be possible. Suggestions of alternatives also welcome. Thanks!