Bad Rated 1 out of 5 stars

Everytime I enable this addon, put it somewhere in my UI and set it up it will randomly freeze my Firefox. Sometimes several times in a row or directly after I started the Firefox. This happened on 2 different machines now.

This review is for a previous version of the add-on (1.4.1-signed). 

I did manage to reproduce (most likely) the problem you are describing - some time ago - by adding another (or two) add-on, can't remember name, but it had to do with feed reading. What happened is the following:

That other add-on would import all of my feeds from Google reader to Firefox, but among those feeds there were many invalid (or not working) feeds.
So my add-on does that: observes for bookmarks changes (in order to have up-to-date items) and Firefox keeps checking those invalid urls and all that concludes to CPU load.
So my advice is: check your bookmarks for invalid - or not working urls. And live bookmarks.
And remove them.