Thanks, Michael, for the update. Do you suppose the folks at Mozilla might have any ideas?
I believe I've described the exact problem earlier, but here's another go:
$ HEAD 'http://luminous-landscape.com/forum/index.php?act=Attach&type=post&id=807'
Date: Wed, 19 Jul 2006 21:37:44 GMT
Server: Apache/1.3.36 (Unix) mod_auth_passthrough/1.8 mod_log_bytes/1.2 mod_bwlimited/1.4 PHP/4.4.2 FrontPage/184.108.40.20635.SR1.2 mod_ssl/2.8.27 OpenSSL/0.9.7a
Client-Date: Wed, 19 Jul 2006 21:37:40 GMT
As you can see, the web server misrepresents the content as "text/html". This has to be fixed in the PHP code, since it's the PHP code that's instructing the webserver about the content in this case.
My guess is that Invision has created a rather complex piece of software, which combined with the site-specific modifications means it isn't very easy to patch to do this correctly.
As for viewing these files:
Internet Explorer has a misfeature (AKA bug) that makes a guess at what something might be if it doesn't look like the content type provided by the web server. That is both stupid and potentially dangerous (it used to be an exploitable vulnerability; maybe not anymore), but it sometimes works. I find this kind of solution unacceptable, so I generally avoid using IE unless I absolutely have to (i.e. Windows Update).
Firefox sometimes plays "nice" and adds the missing HTML tags for you, so that it can render the alleged HTML "correctly".
Opera allows the "save as" workaround.
So as you can see, there is no sane
reason why anybody at Mozilla might give you an answer on how to solve this.