I've tested the issues described here against JAWS 14 and Firefox 16, based on the accessibility updates in the dialog branch: https://github.com/jquery/jquery-ui/pull/794
Basic Modal is now consistent with other demos: DOM content outside the dialog isn't available, both through tabbing and cursor up/down keys.
1. Can access both text inputs and other elements through cursor up/down keys, all content within the dialog is available. Only inputs are tab focusable. This is consistent with regular non-dialog markup.
2. I followed the steps described and don't see the issue described. Focus moves correctly back to the dialog as it should.
3. Can't get outside the dialog anymore. Though even if that would somehow happen again, we now have proper code in place to focus the first input, which applies when moving focus outside the page.
Some of these might have been fixed by updates in JAWS or Firefox, since I tested with newer versions then those available a year ago. Though especially the focus handling is something we improved inside the dialog itself.