When? There have been a few times people stopped using Firefox in large numbers.
One of them was when Chrome first came out. Firefox (and every other browser) at the time ran every site in one process. As sites became more reliant on Javascript, which was usually poorly written, that meant any one tab having a problem made other sites and even the browser’s own UI unresponsive, or sometimes crashed the whole browser. Chrome’s multiprocess model was a revelation. Firefox didn’t get its own implementation until 2016.
Recently, there’s been some movement away from Firefox due to Mozilla making decisions people don’t feel align with open source, the open web, and privacy. The one that has me looking at forks is the planned addition of terms of use to the browser. Terms of use are for an ongoing relationship between a service operator and a user; Firefox is local software I’m operating myself on a computer I own. Its fine for optional online services like Sync to have terms of use, but the browser should work without those.
As I said in the previous comment, state prosecutors would be unsuccessful due to the supremacy clause. State kidnapping laws cannot punish Federal officials for deporting foreigners in accordance with Federal law, or with a good faith belief that they are enforcing Federal law.
Federal court orders can, of course make a deportation illegal, and did in this case. Still, criminal contempt would only apply to officials who knew about the court order, which has not been alleged with regard to the initial decision to deport Abrego Garcia. There was, however a separate order from judge Boasberg to turn the planes around. As yet unnamed officials who knew about that order and had the ability to carry it out discussed it and decided not to obey. They are guilty of criminal contempt.