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.