Just began to use the add-on, seems to work quite well so far! Just one problem I noticed: HTML markup in the description of each field doesn't seem to be parsed and just display raw HTML, thus making the links impossible to click, for example. Here's a screenshot from the description of Facebook:
Compared to the "official" screenshot, text that should be in bold, for example, is just rendered surrounded with "<strong>" tags.
I'm using Firefox 14.0.1 on Linux Mint 13 (based on Ubuntu 12.04). The extension has been downloaded from Mozilla's addons website. I tried using a clean profile and the problem still appears, so it doesn't seem to be an incompatibility with another extension.