1. Accept that you are a hoarder. 2. Stop hoarding. For example, stop bookmarking. Just accept that either you read somethig or you let it slip into the void of everything you'll never read.
For your online stuff, I'd do a mass delete of anything over 90 days old (or pick some other cutoff). You just have accept what's already obvious: you're never going to go through all of it, so why keep it?