The extensions are basically bots to collect info for the user with the extension installed, not steal info from that user. Most are either scraping email, names, and job titles as quickly as a bot can, or mass sending out messages to users based on some criteria.
No, most appear to be plugins for ATS/CRMs, which allow recruiters -- having found a lead on LinkedIn -- to then add them to their CRM. This is profoundly differently.
Here's a video for one of the extensions https://www.youtube.com/watch?v=2XvtuZjblCc (Warning: loud music)