This is why I fake my user agent. I use Qutebrowser (https://www.qutebrowser.org/) but pretend to use the most common user agent on this list. https://techblog.willshouse.com/2012/01/03/most-common-user-...
As a web developer though I know the agent shortcut is tempting. Without it I imagine we'd have to wait for a quorum of popular browsers before dropping feature detection for any given capability.
EDIT: Chrome's user agent doesn't work, but Firefox's does. I suppose it works because if Google's sign-in form sees a Chrome user agent, it expects a certain different browser fingerprint, so it rejects it. But maybe it's more lenient on the fingerprint match if it sees a Firefox user agent. This one worked for me, from https://techblog.willshouse.com/2012/01/03/most-common-user-...
Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:70.0) Gecko/20100101 Firefox/70.0What exactly will it break?
Some examples (there are lots more via IRC/Reddit/...):
https://github.com/qutebrowser/qutebrowser/issues/4302 https://github.com/qutebrowser/qutebrowser/issues/3822 https://github.com/qutebrowser/qutebrowser/issues/1187
> if(browser == firefox) {new_feature_chrome_does_not_support()} else {old_feature()}
instead of
> if(new_feature in navigator) {new_feature()} else {old_feature()}