Here are some really handy tools for when you have to deal with Drupals admin interface:

Autofill -

Automatically fill out forms, great for testing node/add forms with specific sets of data, can store profiles for use on multiple sites.

Edit This Cookie -

Excellent tool for checking out cookies on a site, useful when testing SSOs.

Link Clump -

Right click and highlight a bunch of links then open them up in new tabs, more helpful than you’d think when having to test n number of pages during a migration.

HTTP Headers -

Handy for checking whether pages are being served via Varnish of Drupal Cache. Also great for checking the IP of a server on a HA setup (if setup to output to headers).

Easy Check -

Easiest way to manage Drupals permissions page, click on a checkbox and then drag your mouse and it will auto check all the ones you mouse over, no more clicking like a madman!