Here are lots of links on how to find out what to use

http://stackoverflow.com/questions/2283134/how-can-you-implement-a-jquery-feature-without-having-ie-prompt-users-with-an-ac

Settled in on greasemonkey for Firefox.

http://stackoverflow.com/questions/11569293/what-browser-plugin-that-lets-you-override-html-of-a-website-automatically
http://en.wikipedia.org/wiki/Greasemonkey
http://stackoverflow.com/questions/859024/how-can-i-use-jquery-in-greasemonkey

Debugging – can’t get this working with the latest versions of things.  Another Link and I have given up with Firebug or Web Developer Tools.

suggest loading local js file (does not work – so again – forget local debugging!!) 

Blocked Content warning in Firefox – simply press the shield in the upper left corner of the url.

Storing vars across pages