Automating repetitive Firefox tasks is one way to save your fingers from undue stress. From a sidebar you can toggle on and off, you can run, record, and edit macros. Recording is as simple as pressing a button before starting and clicking another to stop. For more advanced tasks you can turn to a set of intimidating demos, but frankly, we found the Web site wiki and step-by-step tutorials far easier to follow.
While iMacros can theoretically be used to input passwords, we strongly recommend encrypting them and either saving your master password to Firefox or inputting it each time. Being able to save macros as bookmarks and being able to share them via e-mail and Delicious are great features, though we wish we could schedule the macros, including running one or to just after booting Firefox. We also wish we could run macros in the background while we worked on other browser tabs. It's a modest request, but without it, just plan to take a break whenever a lengthier macro runs.