I'd say installing an extension is a pretty big sign of consent. It's named clearly and clearly describes what it does in the first sentence of the description:
> A browser extension to share data about your social feed with researchers and journalists to increase transparency.
I'd call that type of data gathering quite consensual.
You're also granting the extension access to your friends' data, given that it can see everything that you can. Your friends consented to show that data to you, but not to the extension developer. Your friends' consent is not transitive.
When I was a regular FB user I understood when I share stuff with friends that it might be visible to their browser extensions. Ubt I feel your comment is sort of misdirection as the purpose of the browser extension was to collect information on ads in peoples feed. Advertisers might show up in your feed, but that doesn't mean they're your friends, even if you consented to receive ads by signing up with a petition organizer or political campaign.
> A browser extension to share data about your social feed with researchers and journalists to increase transparency.
I'd call that type of data gathering quite consensual.