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Some web-servers intentionally or inadvertently use the application/octet-stream mime-type for files where either the actual mime-type isn't known or when they are incorrectly configured. Or perhaps where the file is binary and application/octet-stream is appropriate.

With these mimetypes, the Open With option is omitted from the file download dialog box.

I would like to modify Firefox mimetype.rdf (or whatever else is needed) to change this behaviour so that "Open With" option is always present.

I have skimmed the Mozilla docs and monkeyed with the rdf a bit, but I am hoping someone has already figured this out.

Of course, if there is an extension I cannot find that just does this already, excellent.

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What OS are you using? In my Windows 7 with Firefox 10.0.2, even application/octet-stream mime type prompted me with an Open With window. but in Linux, I follow the tutorial and nothing works. – Mengdi Gao Mar 10 '12 at 10:35
@MdGao I found this to be happening on linux - the stupid thing is I no longer access the system that was giving me the problem. Do you have a link I can test against? – Paul Mar 10 '12 at 11:58
if you mean download link for test: this, and this – Mengdi Gao Mar 10 '12 at 14:04
In recent versions up to the current 32.0.3 on Linux I have the option Open with but it remembers only a single executable in the pull-down menu so it is very hardly usable when you have to find the right executable file almost every time. --- Unfortunately I did not manage yet to make OpenDownload² working completely as expected (opens .pcapng in gedit instead of wireshark). – pabouk Oct 14 '14 at 17:18
I tried editing the mimeTypes.rdf adding handling of application/octet-stream, but that did not help. – Finn Årup Nielsen Mar 23 '15 at 23:42
up vote 3 down vote accepted

You could try the experimental extension OpenDownload² :

OpenDownload² inserts a "Run" button into the "Open File" dialog when downloading files. Clicking the button saves the particular file in your temporary directory and opens it with the assigned application or (for .exe files) runs the application from there.

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Yeah, it works - not quite what I want, as I'd prefer to be able to pick the app that it uses, but at least it will defer to the OS for file types it knows. – Paul Mar 11 '12 at 1:32
Seems a bit scary that it will just execute a file, regardless of the file type. Couldn't you accidentally run untrusted code if you mistake a exe file for a PDF? – Finn Årup Nielsen Mar 23 '15 at 23:46

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