FEBE and Portable Rated 2 out of 5 stars

I tried everything to get it to work on FF Portable, no luck
And whats with the ugly tray info boxes? Couldn't the maker make a lite tooltip on mouse hover?
2 Stars for the idea though

This review is for a previous version of the add-on (6.2). 

Not supported

While some users have reported success using FEBE with Firefox Portable, it is not officially supported.

From http://portableapps.com/support/firefox_portable#known_issues:
"Themes and Extensions - Most themes and extensions should now work with Firefox Portable -- including those that make use of the component registry. A handful will still fail, though."

The issue is therefore with Firefox Portable, not necessarily FEBE.