Works very well for me.

PERFECTION!

It displays text and that's about it. Jumps to beginning any time you show/hide the interface.

The addon features are nice, the interface okay, the text is good readable and it renders images (something fbreader doesn't). To bad that internal links don't work (like in fbreader) and navigating seems only possible with arrow left/right or mouse scrolling.
Thanks for sharing this addon.

The Good: It's OK. It works.
The Bad: But it's as ugly as sin, and as someone else said, you won't want to read a whole book in it. I don't think it shows any images.
and...
The Ugly: You can't use your keyboard to move up or down through the .mobi, you have to use the scroll bar.

Good: It displays MOBI correctly.
Bad: The interface is just not great.

I would recommend just installing an eBook software on your PC, cuz you won't get through an entire book with this.

MOBI file is stuck on index and can not move to read chapters. Interface is quite hideous

It works just fine, but the interface is ugly and not really intuitive.

I'm giving 4 stars in hope of the author to further improve it. It does show parts of a mobi file so it's working somewhat. I think currently it's having issues parsing separate chapters and jumping between them. Also I believe the right-click thing only works within the browser on .mobi url links, the author should clarify on that. Still, many thanks.

I just installed this. It actually does read mobi files. Clicking on the top right mobi icon loads a window with both an address bar and browse button. Could do with a bit of polish, e.g. close button etc, but it does the job it sets out to.