Rated 1 out of 5 stars
This is by far the best looking and most intuitive UI for changing favicons. It doesn't add loads of stupid, ugly menu items like Bookmark Favicon Changer does.
However, installing Favicon Picker 2 seriously breaks Firefox's tab functionality (and this has been the case for quite some considerable time - it's not something that has only recently happened with the latest version of Firefox).
This is not just a case of an extension needing a simple version bump to get it to work, it has fundamental incompatibilities with recent versions of Firefox.
As long as these bugs remain unfixed then this extension is virtually useless.
Fvicon Picker 2 has really great potential, but until proper fixes come along (to sort out all the tab functionality breakages) then you would be well advised to avoid this.
Not as complete as it could be Rated 4 out of 5 stars
This extension is great, but I wish it could also replace the favicon displayed on tabs and in the address bar, with the user's chosen icon (rather than only working for the bookmark itself).
At the moment you can assign an icon of your choosing to a site's bookmark, but as soon as you click the bookmark you get a totally different icon displayed (the web site's default icon) in the address bar as well as on any tabs that you have open for that site.
It would be more visually consistent if you could select an option that replaced all favicon usage (tabs, bookmarks and address bar) with your chosen icon.