Furl has a public version of single accounts (unless marked private by the account holder) so you can search an individual archive.
It also has a collective search engine of all the Furl accounts, but you have to search this from your own account.
What if you don’t have a Furl account (even though they are free!)
A way around this is to use Google:
in this example “trigon” is the search term
Although it doesn’t accept “phrase searching”…I tried to do a search for “tax and taxonomies” which is an article I have in my Furl archive, but it returned 2 hits from other Furl accounts that had both the words in the bookmark, but not as a phrase.
Another way is using the site search function: