User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.6) Gecko/2009020911 Ubuntu/8.04 (hardy) Firefox/3.0.6 Build Identifier: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.6) Gecko/2009020911 Ubuntu/8.04 (hardy) Firefox/3.0.6 I'm trying to view a file through a link within a web page. For some reason FF thinks it's a BIN file (I'm sure it's just a text) and offers saving that file only. There's not an option for setting up a default viewer for such a kind of 'files to open'. WHY? Reproducible: Always Steps to Reproduce: See details above. Actual Results: Unable to view a file of BIN type straight away. Just save option. Expected Results: I'd like the BIN files to be handled as the other file types. To be able to setup a default viewer for such files.

Firefox thinks it's a binary file, because it probably using the application/octet-stream MIME-type instead of plain/text or plain/html or whatever. There's no way that Firefox wants to open that file, because that MIME-type is used to warn that it's a binary file, not a text-file. Unfortunately, it's also the default for many webservers (like Apache). Internet Explorer tries to determine that it's text, but Firefox can't, since the standard explicitly says that the MIME-type has to be honored. This is not a bug in the browser - the website should only be using files that have a MIME-type configured. Or, the MIME-type should be added in the configuration of the webserver.

The same 'explanation' again. Please, see https://bugzilla.mozilla.org/show_bug.cgi?id=478385 Why do applications try to prevent me from doing what I need? I understand that the application/octet-stream MIME type means unknown data type. What I DO NOT understand is why am I not allowed to set up MY viewer for such data type. I repeat, it's MY responsibility.

Because you think with file extensions but there are NO file extensions for http and email messages, there are only mime-types. Content-sniffing is dangerous, this is an example for IE's sniffing that executes Javascript in Images files. http://www.heise.de/security/dienste/browsercheck/demos/ie/msniff/security_logo.jpg (sorry, the warning is in german)

Matthias, I do understand what you're trying to say. The point is I don't want FF (Thunderbird) to guess what a type of data it is. I just want to have an option for setting up an application for opening such 'anonymous' data. Nothing more. Why is that such a big problem?

You would not asked if you would have searched bugzilla. There can't be a helper application for application/octet-stream because that's unkown binary data and there is no application in the world that can handle unknown binary data for all types. Using the extension from the file itself is also guessing, and that is exactly what you want. Marking as dupe of bug 67940

Hold on. Only thing I wanted was to set up let's say vim as a viewer for unknown data type because from time to time (mostly) it's just an error on a server side and I'm getting a plain text file. If it is not text, my problem and I could have lived with it. And my vim could have survived it as well, I think. However, you're smarter then me and you know better than me what I want and what I'm not allowed to do. Nice. PS "... there is no application in the world that can handle unknown binary data for all types." is a rather silly excuse.