If you develop on Chrome given that it's the largest, then you have the following issues:

- Firefox will render stuff wrong

- Safari will render stuff wrong and something will break

Generally browsers these days are pretty good.

There are some dark corners where there are still differences but these are not in the "I just want to build a website"-level of complexity IME, and are more in the "I am building a large XXX,XXX lines-of-code enterprise SPA used for hours at a time for thousands of users as their primary job across varied OS and browser combinations" level of complexity. E.g. I recently had to debug how different browsers handle cookie eviction for more than 100 cookies under the same top-level domain. This is not the sort of issue you you face with a "I just want to build a website" problem.

I unknowingly relied on undefined behaviour in JavaScript Array.sort; worked fine/as expected in Firefox but then got bug reports that turned out to be Chrome/Safari.

Not just dark corners IMO.

Interesting - what were the details? I've never heard of this and rely on this feature all the time so please do share the reproduction so we can all benefit?

    > [2,1,3].sort((a,b) => a < b)

Sorts in Firefox (gecko), but not in V8. (resp. `a > b`.)

FF:

    Array(3) [ 3, 2, 1 ]

Node:

    [ 2, 1, 3 ]

(Obviously that's a silly example because you'd just `.sort()`, I think I was doing `a.id < b.id` or something, but it's not a significant detail.)

You can even reduce the reproduction to `[1,2].sort((a,b) => 1)`. Have fun..!