Also, clipboard data access. With Opera's switch to chromium, Firefox was the last browser without programmatic access to the clipboard[0] (though as usual MSIE has a non-standard implementation) so you had to listen for the paste event and post-process whatever garbage had been dumped in your paste area (and of course couldn't access high-level media types)
[0] Opera, as far as I remember, has neither clipboard access nor a "paste" event, the POS.
Yes and no, the website can access clipboard data specifically when you're pasting as a user-triggered operation (C-v/M-v or "Paste" from a contextual menu) (that is the clipboard data is only accessible from the `paste` event).
This allows an application to access alternative representations (the clipboard can store multiple representations of the same data e.g. text and html and image and whatever, and the application can then pick the most appropriate — or all of them) and to pre-process clipboard data before inserting it programmatically. Very useful with e.g. RTE. Arbitrary clipboard access most definitely isn't allowed.
In firefox, probably by going to about:config and setting `dom.event.clipboardevents.enabled` to `false`. In webkit and MSIE (which have had the feature for ages) I have no idea.
No, not unless you initiate a paste operation manually (literally, as in by hitting ctrl-v or etc.)
This is one of the ways that pasting images from your clipboard into, say, an image hosting site can work.
I had a difficult time finding fuller explanations of the capabilities - mostly because there isn't a standard API across browsers yet - but here[1] are the relevant Safari docs.
There's also a working draft[2] from the W3C for a standardized API.
[0] Opera, as far as I remember, has neither clipboard access nor a "paste" event, the POS.