Well, and being able to get at your bookmarks from anywhere, and being able to attach searchable descriptions/tags to the bookmarks so you can find it even if the page title or URL isn't memorable.
Firefox bookmarks support tags, keywords and descriptions. Plus it syncs (encrypted end-to-end), so you can get them anywhere if you can use Firefox from that place.
I use both browser bookmarks (Firefox) and Pinboard. I think they're complementary rather than one being a replacement for the other.
I use browser bookmarks for pages I visit often or intend to return to fairly soon. I use Pinboard for long-term archival where link rot is a real concern.
