Great but with 1 minor caveat Rated 5 out of 5 stars

Most of the time, this extension is great. However, anyone attending on-line college classes which are using Desire2Learn (D2L) will find that this extension screws up the use of that system. D2L is very much Java-centric and this extension will cause certain functions in D2L to simply hang.

This review is for a previous version of the add-on (2.8.7). 

Unfortunately Desire2Learn is closed source and not even an approved Mozilla software!
Thus there is nothing I can do in order to fix the problem and only the Desire2Learn company is able to provide support on this or similar issues.
Anyway, thank you for reporting this!