Thank you!

Ah, so "Create an account" means "Sign up for a group"? I didn't make that connection at all.

I'm on desktop (Windows) and here's the bottom of the page.

Here's the whole page in PDF. chirp-social-page.pdf

On the chirp.social page it says:

How does this work?

1. Create an account on this page.

There is no "create an account" link. Nothing on that page seems to be related to creating an account.

+1 even if belated!

I don't think you should deprecate this property because not all the browsers are playing nice.

jQuery hasn't deprecated this property, the browsers have done it. In jQuery 3 and 4 we just pass through what the browser gives us. If the browser which value is wrong, we would need some other reliable source of information to be able to synthesize a correct which value. That would usually be button or buttons I'd think?

One example is the middle click on a mouseup event in Chrome. I did not get a value of 4, but instead a value of 2.

That sounds like a bug in Chrome. You should report it to them and include a test case. If you can put a link to the bug report here that would be great.

The which property is set up here which basically just lets jQuery lazy-retrieve it when needed (see addProp).

There isn't any normalization of this property because up until this report all supported browsers returned correct values. The Mozilla docs indicate that event.which is deprecated, so perhaps Mozilla no longer is returning valid data in some situations. I'd call that a bad compat choice on their part, and you could report a bug if they're the only ones that have bad values, but the property is deprecated and they have documented this very bug in the "Compatibility Table" section (click the * in the Firefox cell).

For "new" code (like, written in the past 10 years or so that event.button and event.buttons have been in modern browsers) it would be best to use those instead.

I don't see that event.which is documented as being returned by a mouseover event. https://api.jquery.com/event.which/#event-which1

Is there some native property that gives you the button that's down?