Framing by using any other means than border-radius is extremely expensive, it's almost certainly not going to be a good trade off to fix this just in case people are using applets/other objects in FF.
Twitter - @evantrimboli
Don't be afraid of the source code!
I agree that moving FF back to the table / image based cornering across the board doesn't make sense, but I wonder if doing it for floating items (windows, tooltips, etc) should be the norm as it is much safer. As there are very only a small number of floating items on screen usually this shouldn't really impact performance. I wouldn't want it to be the default behavior for controls that may appear a lot, such as buttons, though!.
I know 4 still still uses the tables / images approach with IE - is there a way to force this on a per class basis for other browsers?
We unfortunately need to make heavy use of applets to to data exchange with applications on the users local machine and the fact that everything looks so poor in Ext JS 4 (and perfect in 3) is a huge problem for us.