I like this extension, thanks a lot! I first deleted the file favicons.sqlite and then ran it. Once it was completed I did a first clean-up, which was needed, since there are bookmarks there, which I didn't use probably for 10 years.
I noticed however that not all Favicons are loaded, while the same ones do show in Google Chrome, how come??

However it might be handy to write a little instruction how to run this add-on, since it took me a while to figure it out and thanks to reading the reviews I was sent in the right direction where to look.

Update:
I found the sidebar back in my customize menu, where I must have put it a few months ago when I first used it. I just didn't recognize it as this app, since it was called "sidebar" :)