[samwillis]

Safari and WebKit had it from 2008 but prefixed. Chrome, back then based on WebKit pre forking it, will have had prefixed support from launch.

Firefox had it from 2006, prefixed.

IE was the holdout, not having it until v9 in 2011.

https://caniuse.com/border-radius

[achairapart]

Yes, border-radius was available since ~2007/2008 except for IE (I remember using some hack involving HTC files, maybe CSS3PIE[0]).

[0]: http://css3pie.com/