Close, but not quite Rated 3 out of 5 stars
This is a very interesting idea for an add-on, but it's a bit too cumbersome to use. It feels kind of like the designer has forced his own workflow on to the users of this add-on. For instance, the feature to add a link and automatically fetch a feed is really splendid. However, the fact that it automatically renames your note to the feed title is a nuisance, particular if the feed title is something generic like "blog". I've tried renaming the note title but it always reverts.
The interface is definitely a bit clunky too. Re-positioning notes is wonderful, but I don't want the reposition-maximize-close context menu to pop-up every time I mouse-over a note because that's distracting. If those things were accessible from a right-click on the note, it would still be intuitive but out of the way.
Lastly, the toolbar is really just glaringly ugly and distracting. I wonder why it's even necessary. And the built-in google search (that opens in a new window) is not only unnecessary, but also completely non-functional. (who opens up search in a new window 100% of the time?)
My last gripe is the built-in tab navigation. Firstly it looks out of place since it's styled completely differently from the rest of Firefox. Second the way it's styled is pretty ugly as well. Again, I don't want the red "X" button glaring at me the whole time. And I don't want the tab to always be waiting for me to rename it. Once I've renamed it, it's probably going to stay named that way for a while. And again, a right-click is still intuitive and keeps it out of the way.
The overlay on a window is an interesting concept and could make sense for some people. I could even see myself using it like that. But personally I'd prefer to see fireNotes run in its own tab (which I'd then make into an app tab, like I do for ScribeFire). The overlay is fine though, so it would be nice to see "run in tab" as an option.
All in all this is a decent add-on with some promise. I'm sure some people could get some use out of it. But for me it's just too clunky and distracting so I feel like it would inhibit my work more than aid it.
I really want to thank you for your detailed review and I totally agree with almost everything you said.
As I am really more a developer than a designer I think especially your critics about the UI is useful.
Unfortunately I don´t have a lot of time at the moment due to my studies so I can´t really work out the problems, but I´ll try to do so as soon as possible.