Comment by quacksilver

Devs, particularly those with pressure to ship or who don't know better, unfortunately see 'it works in Chrome' as 'it works', even if it is a quirk of Chrome that causes it to work, or if they use Chrome related hacks that break compatibility with other browsers to get it to work in Chrome.

- Sometimes the standards don't define some exact behavior and it is left for the browser implementer to come up with. Chrome implements it one way and other browsers implement it the other way. Both are compatible with the standards.

- Sometimes the app contains errors, but certain permissive behaviors of Chrome mean it works ok and the app is shipped. The developers work around the guesses that Chrome makes and cobble the app together. (there may be a load of warnings in the console). Other browsers don't make the same guesses so the app is shipped in a state that it will only work on Chrome.

- Sometimes Chrome (or mobile Safari) specific APIs or functions are used as people don't know any better.

- Some security / WAF / anti-bot software relies on Chrome specific JavaScript quirks (that there may be no standards for) and thinks that the user using Firefox or another browser that isn't Chrome or iOS safari is a bot and blocks them.

In many ways, Chrome is the new IE, through no fault of Google or the authors of other browsers.