Comment 15 for bug 240133

Ian, somehow we must remember that we have an MHTML document if we don't want to
rewrite its links. URIs in MHTML documents can be the same as existing URIs
outside the MHTML document. If we rewrite the links (e.g. convert them to <cid:>
URIs) it is very likely that we break at least some JS.

It may be possible to keep the original URI for the root resource, but it would
require more changes to docshell. I do not intend to implement this in the first
step. Please file a bug on it once MHTML works.

If we display a resource other than the root resource (e.g. open a frame in a
new window), it does not make sense to keep the original URI and it does not
make sense to show the given URI, because the displayed document may be
different from a document with the same URI retrieved directly over the net.
Another approach would be to generate a Content-ID ourselves if the MHTML
document doesn't specify it and use <cid:> instead of <mhtml:>. But that would
be much more difficult to implement.

Name of the protocol: We do already pollute the protocol namespace (<jar:>,
<view-source:>, <about:>, <internal:>, <chrome:>, <resource:>, <javascript:>).
But if you think we shouldn't continue this it would be no problem to use
<moz-mhtml:>.