https://addons.mozilla.org/en-US/firefox/addon/recoll-indexe...
The one complication I found was ensuring that I blacklisted sensitive websites such as banks.
I'm sure there are security/privacy trade-offs. Storage is not such a big thing. I found that index size leveled off somewhat after a point. It probably would use enough storage to make it unreasonable for mobile browsers.
This would be a good additional feature for Pinboard perhaps (which I've been intending to subscribe to for ages but never get around to).
It would be a good feature for the deluxe Pinboard subscription. As long as you're mirroring the content, you might as well index it with Lucene or something.