Frecency

For example, a feature called "frecency" compiles the user's browing^([sic]) history to suggest similar websites and searches.

[…] the AwesomeBar will match what you’re typing (even multiple words!) against the URLs, page titles, and tags in your bookmarks and history, returning results sorted by “frecency” (an algorithm combining frequency + recency).

So the more often and the more recently you’ve been there, the higher “frecency” it has and the higher it’s rated.

[…] or improve our cache performance so that we're keeping cached items that are related to sites with high frecency -- […]

No, Tb [Thunderbird] has yet to develope^([sic]) the Fx [Firefox] frecency thing. It's just simple pattern matching, IIUC.

Regarding collection usage, frecency metrics are employed, combining frequency and recency, to effectively capture concept drift and temporal trends.