In Opera, for starters:
- add option to warn user when closing a window when there are 2 or more tabs open. really, accidents do happen. firefox and safaric have this feature all along and even though I've requested of this before, still nothing.
- do not reuse tabs for certain things, such as clicking Help->About Opera. or better, just provide options to disable such behaviour (for more smooth transition).
For Firefox:
- is the stupid "feature" of using (unlimited) temp files for random seed still present in the latest stable version? remove it!