Right now the UI of Firefox and Thunderbird are a complex mess of iterations of previous versions. There are so many elements left over from previous versions that have not been updated, or do just not fit in with the overall design scheme. Opera has...
It would be great if there was a better UI when dragging a tab across the screen and/or into it's own window. The current animation is clunky and hard to follow. It's much easier to drag and drop a tab into another window or into its own tab on Chrom...
