I never used live bookmarks, but I did find the subscribe button handy on RSS/Atom feeds - I wonder why that part of the codebase is hard to keep.

These days I am using FeedBro[1] but I don't like that it isn't open source and has poor/non-existent keyboard navigation support.

I used to get on well with NewsFox[2] before Mozilla killed legacy extensions.

[1]: https://nodetics.com/feedbro/

[2]: http://newsfox.mozdev.org/