Rated 5 out of 5 stars

The great (and smart) thing is that the developer used what is already existing in FF to offer a new functionality. From a privacy point of view this is an extension that will not expose the history to someone else than the one able to log into the FF on the computer. No need to use an external database hosted somewhere on the net. And something makes is event more interesting : you can load it in FF only when necessary : save the XPI on your disk, install it in FF and desinstall it when finished. The next time you need it you can reinstall it, it will work perfectly.
I received a warning about a script taking too long to execute, when I searched for a specific page : the extension had to build the tree and it can take a while. In that case do not interrupt the script. At least not yet : give it a chance to finish the data crunching ;-)
As an improvement I'd like to see a kind of "temporal filter" in the tree, or a way to set a "window upon history" to limit the scope of the results. Say you want to track the history to/from the 02/02 : you could exclude the pages visited in January or in the other way, exclude the ones after February. It would allow trimming of the "tree branches" that one feels are of no interest. You could also have the possibility to set a "not before but after" date interval... Still, it's a great addon as it is. I hope it will be updated to match the FF updates :-)

This review is for a previous version of the add-on (0.19.4).  This user has a previous review of this add-on.

Thanks a lot for your experience sharing and great suggestion. I'll add some form of "temporal filter" first (likely in Jan 2011). To address the time-consuming searching issue (causing the warning) --- a problem from the start --- besides optimization I'm thinking of showing the searching results incrementally, and making the searching process manually interruptible. That's going to need more effort.
Thanks again for the detailed comment and encouragement. It's a nice new year gift for me.