I've used it for more than a year now and am very satisfied with it. As the Rambler said, it is not without the occasional fault but for the most part it works very well. Not only in Firefox but all browsers I have installed (IE9, Chrome, and Opera), as well as FeedDemon and other apps that use the IE browser internally.
The latest version has a new feature that kinda sucks - no more context menu item for Ad Muncher but instead a drop-down toolbar that does not have all the same functionality that the menu had. I don’t like it much but they say it will improve. The reason for it is that the constant browser updates (read: Chrome and Firefox) tended to break many extensions, requiring a lot of upkeep. This toolbar overcomes that problem according to the developer. Makes sense as long as they can make the damn thing at least as functional as the context menu was.
BTW, I purchased AM as a Pro license - I believe on Bits - and soon thereafter upgraded it to a lifetime license. That should speak somewhat to my confidence in it.