For firefox, i use https://addons.mozilla.org/en-US/firefox/addon/personal-bloc... . It puts a "block this domain" link under the result (gotta block each pinterest.* though).

But if you blocked each bad result, I'm not sure there'd be any good left.

For example, I search "a bougainvillea without pruning" and all the results are "how to prune bougainvillea". Try: "How do I search the web without e commerce results?" and all you'll get is "how to do ecommerce better" pages.