An excellent update Rated 5 out of 5 stars

You really put in a lot of good work. I especially like the way you have streamlined the interface while keeping the old look as an option; also the option of adding user defined style sheets is great. I like the way you keep the important information of the URL path visible, while color coding the various elements, so this makes it a very useful addition both for web users and developers alike.

This review is for a previous version of the add-on (3.0.1-signed). 

Rated 4 out of 5 stars

This is a good usability feature, the dropdowns add real value. I don;t care for combining the bookmarks in the address bar too much, as this simply makes it too crammed.

It should _not_ however treat the querystring the same way as the other parts of the URL, as the qs variables are really not "levels" but just a flat list. IMO anything after the file name must remain the way it was originally; e.g. > search.html?category=antiques&item=Clock&pages=3

Or you can add more value by providing a collapsable editable listbox with querystring items. Also in-page anchors (#) should probably have a different character than > and the URL should not always end with > because you do not know whether you are looking at a directory or a document. 4 points though for the very useful features within the main part of the URL.
It would be nice to have some proper chevrons (instead of using the ugly characters > and v)

This review is for a previous version of the add-on (2.5.1-signed). 

I highly appreciate your input. As far as querystring is concerned, an address for a page can have all sort of complexities, for ex. in any forum, that querystrings actually do refer to levels i.e. Main forum>Sub forum>Post>(Reply/comment). That is why the querystring is greyed out a little. I'll think of something more useful.
About the editable listbox suggestion, I will look further into it and certainly consider it for the next major version.
I will see whether the chevrons are supported in all types of encoding etc. (I had better symbols for both > and v but they were showing up once inside the urlbar)