> Thunderbird delivers RSS feed items the same way as email, so you can apply filters to mark them as "read"

This is a good idea. I use Thunderbird only for a small number of feeds I want to read every post from. I used to also use a separate feed reader for my "river of news", but eventually I stopped looking at that and just loadded hackernews or reddit when I wanted a distraction. But I might try Thunderbird for more feeds and just auto-mark most of them as read so I can browse at my leisure.