I write greasemonkey scripts that add extra fun stuff to Jira. They aren't pretty but they make Jira prettier and easier to read.

http://userscripts.org/scripts/show/27838 - Comment Highlighter
http://userscripts.org/scripts/show/57196 - Change Combiner

On of the things that annoyed me was that whenever I'd make a change, all content being reset back to it's initial condition, before my script had run. So I'm using the following code to hook JIRAs refresh event to tell my script to run. One small problem: What happens when you change the active module ("All", "Comments", "History", etc). I haven't found an appropriate event to bind to, none of the events in JIRA.Events get triggered.

unsafeWindow.JIRA.bind(unsafeWindow.JIRA.Events.ISSUE_REFRESHED, function() { run_amok(); });
run_amok();