They used to be owned by Evidon Inc., later renamed to Ghostery Inc., which was a classic ad company (sold data gathered from the opt-in GhostRank feature to help other ad companies figure out how to not have their ads blocked).
Nowadays, the Ghostery extension is owned by Cliqz GmbH, which is still an ad company, but they specialize in privacy-conscious ads (mainly ad personalization based on evaluating browser history locally), have a privacy policy that has no holes as far as I can tell, have all of their client-side code open-sourced and they are even minority-owned by Mozilla, so Mozilla can at least check over what they're doing and would probably give up ownership should Cliqz infringe on privacy (even if you think Mozilla itself is the devil, they would still likely do that for PR reasons).
So, I do think it is nowadays fine to use Ghostery. I still don't quite understand why it's so popular, there's tons of other tools for the same purpose (for example Disconnect, Privacy Badger, Firefox's built-in Tracking Protection), but yeah.
Nowadays, the Ghostery extension is owned by Cliqz GmbH, which is still an ad company, but they specialize in privacy-conscious ads (mainly ad personalization based on evaluating browser history locally), have a privacy policy that has no holes as far as I can tell, have all of their client-side code open-sourced and they are even minority-owned by Mozilla, so Mozilla can at least check over what they're doing and would probably give up ownership should Cliqz infringe on privacy (even if you think Mozilla itself is the devil, they would still likely do that for PR reasons).
So, I do think it is nowadays fine to use Ghostery. I still don't quite understand why it's so popular, there's tons of other tools for the same purpose (for example Disconnect, Privacy Badger, Firefox's built-in Tracking Protection), but yeah.