When I embed an iframe in Opera, it seems to run in a separate thread, so that I can use the iframe to show the progress of a loop in the parent page.

Safari seems to do something similar.

No other browsers do this with iframe, that I am aware of, although you can do something similar with IE using its mode-less dialogue boxes.

Given that Chrome opens up different processes, it does not seem to do so for iframes (when I check the task manager).

Would it not be useful to have iframes running in something that looks like a separate thread / process, like Opera and Safari?