This is a great idea. It is actually similar to a feature of IE4/5.
It is possible in IE to add extra context menu items using Javascript.
This is much more useful than it might appear, for example the
following allows me to have 'Open Frame in New Window' which is not
present in IE4:

<SCRIPT defer>
open(external.menuArguments.location.href);
</SCRIPT>

Of course, this being windows, you also need to (slightly) hack the
registry. IE's approach is slightly inflexible however because you
specify the contexts in which the menu item should appear using a set
of (undocumented) bit flags. This means that embedded objects cannot
create new contexts (though plugins are responsible for their own
popup menus so they can provide that (but they can't access IE's own
context menu of course!)).

AFAIK the only way to do this in IE is via scripting, so an invisible
plugin cannot do this directly which is a pity. For example it would
be nice if Gozilla was able to add a menu item for links saying 
'Download using Gozilla'.

On a related note: Would anyone find a list of features in IE4/5 that
aren't there in Konq useful? At the very least this may generate some
ideas (though we're not short of our own!). I am refering specifically
to the browser UI, not to features of the HTML components. I have to
try stuff out in IE4/5/Netscape/Opera/Konq/Kfm... for work sometimes
so I am pretty familiar with them all.

Rich.

-- 
     Richard Moore		rich@ipso-facto.freeserve.co.uk
http://www.robocast.com/	richard@robocast.com
http://developer.kde.org/	rich@kde.org