There was a question raised but not really answered about "what do these extensions what with all this browsing data?" - while it may be that they're used for direct ad targeting (like real time ad buying against your IP address) it's more likely that they're selling "click stream" data.

In its most innocuous form, this is stuff like SimilarWeb (which is like a more advanced Google Trends), but in the B2B world, it's also custom enterprise reports that are like "how many people that use our bank at xyz also use any other bank at this array of domains and which are most common?"