I will be launching a "Firefox 100" webcompat experiment on Nightly this
week to test whether sites break when they see a User-Agent string with
a three-digit Firefox version number. Nightly will hit version 100 in
March 2022. Chrome will hit version 100 about a month before Firefox.
50% of Nightly users will get a "Firefox 100" UA string for four weeks.
I've been browsing with a "Firefox 100" UA string for four months and
only found one broken site: Slack's emoji button was broken, but has
been fixed: https://github.com/webcompat/web-bugs/issues/67866
If you find a broken site, please file a webcompat bug on