If you can't download or install it's NOT the developers fault! Rated 5 out of 5 stars
People read the instructions before complaining.
If the add-on doesn't download/install often this has nothing to do with the add-on extension itself.
Make sure you have "Accept third-party cookies" enabled, or add a cookie allow exception for "mozilla.org" before giving the developer a bad review or rating that is NOT under their control.
This is an excellent add-on for FF offering control over its function and is discrete.