As you said, using the base name of the URL path works reasonably for
URLs. lynx does that, but Mosaic for X doesn't. Until more browsers
do this simple thing, I can't see us getting far with "name=" (which
is a fine idea).
I made an attempt at making Mosaic use the basename, but the !Y#^%@&
Motif file dialog doesn't seem to have any clue about default save
names. Maybe some Motif wizard could kludge it in, but the best
alternative I came up with was a "save as foo.gif" button. Haven't
got around to implementing it. I can certainly see why X Mosaic
doesn't do "this simple thing" :-)
Alternately, one could add a "Document-Name: " header. Same difference,
but maybe an extra header is more MIMEish.