Rated 4 out of 5 stars

As others have noted, this extension is currently not functional due to a change to the JavaScript functionality in Firefox 44. This was a "breaking change" that was expected to impact many addons, but needed to be done at some point.

Github user @InternalError503 has produced a patch for the breakage in about:addons-memory under Firefox 44+, and submitted it on github. There's no word yet from Nils (the author) about when or if a new version of the addon might be released with this fix, but it's only been a few days:
https://github.com/nmaier/about-addons-memory/pull/23

This review is for a previous version of the add-on (10.1-signed.1-signed).