Rated 5 out of 5 stars

Unfortunately, the extension does not work with the Developer and the Nightly version. The data source is not read and you can not manually import the data as well. Please fix this error, then I will give you 5 Stars .. thank you
Edit: Thank You. With 2.1.5.1 all is fine... 5 Stars :-))

This review is for a previous version of the add-on (2.1.5.1-signed). 

Hi there - sorry about that. Please try version 2.1.5.1 which should address the FF35+ incompatibilities:
https://addons.mozilla.org/en-US/firefox/addon/reminderfox/versions/?page=1#version-2.1.5.1