I went and checked and have discovered I'm the resident browser hipster.
Ecosia.
It's a reskinned version of chrome or chromium or something where your default search engine is Ecosia. The Ecosia search engine is just Bing reskinned and the ad revenue you generate goes towards planting trees!
I've been using it for quite a while, I'm probably responsible for a couple hundred new trees at this point, if not more. They keep a running tally for you but I've used the search engine on multiple devices and haven't bothered to see if you can synch the tally across all of them.
The entire project is up to 175,500,000 trees so far.
I don't know why it would be any good to have a browser reskin just to change the default search engine. It's a simple settings change. Is there any other benefit? Worst case, it becomes poorly maintained and a security risk.