This addon is important because Mozilla has abandoned free and open web technologies.
They've deprecated Livemark RSS/Atom feed reading to be removed by Firefox 63. They are now going to be pushing Pocket, which is a proprietary technology that they purchased, with the belief that focusing all their efforts on that will get them beyond 5% overall browser marketshare.

As of August 2018, I've found this addon has stopped updating[0] for me. Similar behavior to how I found Foxish in Chrome to function years ago. I'll update my review as things change, but I'm close to abandoning Firefox altogether after 16 years of using it, since it was Phoenix. The only thing left are containers and the dedicated search bar.

UPDATE 10/17/18- all problems resolved. This is now better than Foxish ever was. Changed rating to 5 stars.

[0]https://i.imgur.com/8U43aY8.png

German special charakters like äöüß can not be displayed yet.
For example this feed: https://rss.golem.de/rss.php

Also a site visited marker would be an awesome feature.

Great replacement for live bookmarks. There were some issues that got fixed, now the only missing thing is highlighting of unread/new feed items, but it will eventually be added too.

Very good replacement for disappearing Live bookmarks feauture from Firefox core!

Additionally to integrated live bookmarks, this extension also show favicons for each item, and can be used as shared bookmarks folder for team, eg for create quick links to corporate services, deployed from company sysadmin to all company empoyees.

Unique in way they open and scroll like regular items in the bookmarks menu just like Live Bookmarks did. Other rss reading add-ons I've seen/used open in the sidebar, page, or panel which requires more clicking and/or manual scrolling. I find the Livemarks way more efficient for feeds that have many items and are frequently updated. Includes option for refresh interval and ability to import/export feeds (or add them by entering feed url in Options dialog).

Issues:
* Settings dialog seems excessively slow to load.
* Would it be possible to add some way to distinguish between read/unread items? (Live Bookmarks did this and it's the only major missing feature; 5 stars with that ability added.)
* Is there any method to change the default folder to one located on the Bookmarks Toolbar instead of the Bookmarks Menu? (Edit: You can just drag the folder to the toolbar and it still seems to work fine.)

Update: Above issues no longer affect me with current version. Big 'Thank You!' for the read/unread feature.