Not always, we pay for a plugin for Thunderbird (ExQuilzilla) though. We're primarily working on Linux systems so it makes no sense to even have Outlook or Windows in our office. We don't make up a large demographic of our company (which is in the F500 range), but I wouldn't be surprised if there's other places that do the same.

It's a shame Firefox doesn't sell a developer ready IDE, I'd subscribe to that myself if it means better MDN and that the dev tools team is better funded, and Firefox in addition to other donations from elsewhere, throw in a VPN subscription to sweeten it for most people. I'm ready to pay for anything that funds Firefox directly.

I've even seen some in QA who do have Windows just installing Thunderbird.