Karl Dubost works on web compatibility at Mozilla and writes about browser user agent strings, devtools history, and compatibility bugs.
HN links it for posts on capping the macOS user agent string, a list of Google web compatibility bugs in Firefox, and a devtools timeline.
http://www.otsukare.info/2014/10/28/google-webcompatibility-bugs-list has a more complete rundown of the still-extant issues in case you're interested. The whole post is well worth reading, because it does say something important that needs to be said: there are many individuals at Google who believe in things like interoperability, web sites working in all browsers, etc, and strive for that (sometimes against internal opposition). It just happens that Google as an overall organization cares a lot more about its sites working in Chrome than it cares about them working in other browsers, with predictable results.
Mozilla froze the macOS version in User-Agent strings past Catalina too, also due to web compatibility issues (particularly with older versions of the Unity game engine).
Other engines do the same as well: https://www.otsukare.info/2021/02/15/capping-macos-user-agent
>Firebug brought the concept to existence in the first place.
There were other browser "dev tools" before firebug.
https://www.otsukare.info/2020/08/06/browser-devtools-timeline
This is a problem with Google only making things work with Chrome. http://www.otsukare.info/2014/10/28/google-webcompatibility-bugs-list
There are a few google related ones in Karl Dubost's list:
http://www.otsukare.info/2014/10/28/google-webcompatibility-bugs-list
Follow up meeting discussion:
https://www.otsukare.info/2021/03/02/capping-user-agent-string