Rated 4 out of 5 stars

Edit:
I find it a bit rude of you to imply I am unable to read. The poor placement of the version information on the addon page made it easy to overlook. That said, I apologize and have removed the misinformation from my review.

I really like this addon and the functionality it provides. It is evident that a lot of work went into this, and I appreciate that.

Overall, I find the UI quite tasteful, but two minor quirks are leaving a bit of a sour taste in my mouth.
1) I am not a fan of CSS3 text shadows and would much prefer bold text to indicate selected feeds and groups.
2) Icons on the feed entry list are not aligned in a straight line when both short and long timestamps (e.g. "11:20" and "03/03/2015") are present, which is somewhat displeasing to the eye.

Last but not least, I find the lack of sync capabilities rather disappointing.

With these little annoyances removed, this addon could easily be a 5/5 for me.

This review is for a previous version of the add-on (2.1.2.1-signed). 

I regret that you are not able to read informations available on this page (see version information).
EDIT: *able to find (sorry for my awkward english)

Bamboo is an open source software.
All sources are available in the add-on file.

The development process is not collaborative and do not use tools like GitHub because i do not have enough time for managing contributions.

You could customize the add-on style without creating your own version by using your userContent.css file.
@-moz-document url("about:bamboo")