The border of a div with 'border-radius' applied looks not as good and sharp rendered by Firefox 3.x. I think/hope, this should not be that hard to fix... Cairo can do a lot better;) Here's some test: http://www.css3.info/preview/rounded-border/ I apologize, if this was already fixed in some newer versions. I was not able to build WebKit from GIT...
I just played around with PyCairo and tried to reproduce WebKit's rendering of rounded corners. I translated the code from WebCore/platform/graphics/cairo/GraphicsContextCairo.cpp's `strokeArc()` (l. 380) into Python (attached) and got a normally rendered corner. I changed the antialias-settings and line thickness to make it look like WebKit's rendering, but I didn't get it. If the rounded rect's corner is drawn by `strokeArc` (I just can't cope with WebKits 500,000 lines of code... So... I'm not shure...) I suppose, that the problem is something else and not located in this method. I'm writing a widget system for my own little desktop environment and need the border-radius setting for designing the widgets. It just looks ugly. If there is any way to help you I would love to do so...
Created attachment 45534 [details] Python test case.