Last December at Qualcomm's Snapdragon Technology Summit, the company announced that both Chromium and Firefox are coming to Windows on ARM, running natively on ARM64.
This aims to solve a major pain point of Windows on ARM, which is that browsers generate code in real-time, so they can't be cached and they're harder to emulate. In other words, you'll really want them to be running natively, rather than using an emulated x86 browser.
At the time, the only native browser available was Microsoft's Edge, but Firefox started publicly testing ARM64 Firefox less than a month later. Microsoft also announced that it's rebuilding Edge from Chromium the day after Qualcomm's announcement, and it seemed like everything was coming together.