Rated 5 out of 5 stars
What once awakened my love of the computer was the day my mouse broke, and I needed to learn to use a computer without one. Twenty years later, at a time when every webpage and program expects you to use a mouse to do everything, this plugin is a breath of fresh air.
As a developer by day, the best tools in my kit by far are the console (in my case, PowerShell), GVim, and Firefox + Pentadactyl. I've had a love/hate relationship with FF over the years, but this plugin is THE REASON why I continue to use it. In addition to making repetitive browsing easier (I remember the hint numbers for several elements on frequently-browsed websites), I find that I can browse the web with far greater ease using this plugin with infrequent mouse usage. The learning curve is steep, but for vim users it shouldn't be long before you pick it up.
Among my favorite features is the use of a third-party text editor for compositing (CTRL+i in a text field or textarea), a feature that is sorely lacking in other browsers. Performance seems to lag somewhat (even running FF, cache, and profiles on ramdisk), but it easily pays for itself with productivity.