Oh, the boundless optimism. How cute.

Oh, pointless condescension on the internet. How cute.

More recently, though (especially, the last couple of years), browser vendors work very closely with standards groups, contributing there, and looking for feedback from other browser vendors. At least in the CSS and JS space, the extensions to those standards have proceeded largely as a group effort rather than as you described.

The browsers have started to first ship things behind feature flags, and in Chrome's case also behind "Origin trials". We just have less need now for one browser to go off and define their own way for borders to be drawn as rounded rectangles.

I suspect we'll see some funky CSS extensions ship pre-standardization for VR headsets, though. Things like controlling the z-axis height of <dialog> and other elements.