Good RSS Reader but needs user configuration. Rated 4 out of 5 stars
I revisited this add-on after the initial "OMG Google are closing Reader" hysteria. Importing OPML from Google doesn't put it where you expect it, this is due to Google's folder structure.
Works well, is lightweight and quite fast but does need configuring via it's options menu to monitor the correct bookmarks folder for feeds. There is also an option to configure the appearance of the rendered feeds via stylesheets allowing you to have a one or more column display.
When subscribing to a feed in Firefox it works better if you choose Live bookmarks then save in the folder that Sage is monitoring.
If you're prepared to spend some time configuring and making yourself familiar then you'll find it quite a useful RSS reader.