I haven't followed exactly where they landed on this but both Firefox and Chrome have been testing user-agent strings with version 100+ for a while, and have (or at least had) a fall back mechanism to present the version as 99.xxx where the xxx contains additional information with the true browser version. There's also a longer term plan to phase out User-Agent headers as they exist now, more details at https://blog.chromium.org/2022/03/chrome-100-beta-reduced-us...
eklitzke|3 years ago