Lots of people have been doing this style of web mashup for a long time. Things are now stable enough, even in FF3, that you can jump in and get ramped up super-fast.

  • Install Firefox, along with Greasemonkey and Firebug addons.
  • Grab a starter script from here, save it as [myscript].user.js, and open it in Firefox (Ctrl-O) to install it.
  • Bang on it! Change the script to do your bidding…
    • change the target website
    • browse around for DOM objects to mangle with Firebug’s Inspect
    • you can do cross-site xmlhttprequests, whoop!
    • reload by simply reopening the file and refreshing the page
  • Compile the script into a FF addon in one easy step, here.

Bring all your honed software development skillz, or things will get messy fast. Get mashing!

Also check out chickenfoot for another way to go.