Handling of known MIME types and application/octet-streams is inconsistent



16 years ago
10 years ago


(Reporter: wolfson_uk, Assigned: mscott)


Windows 98

Firefox Tracking Flags

(Not tracked)




16 years ago
... which leads also to the problem that helper applications can not be used
efficiently at all.

This problem shows e.g. with JPEG images (but I had them with different types of
files such as .asf and .wmv video streams as well).  I have defined my helper
application, so that JPEG images from email attachments should be opened with my
default image viewer, but with the requester opening to choose if I want to open
or download first.

Two problems here:
1. If the mail with the JPEG image comes from a different emailer, the image is
often recognized as an "application/octet-stream" file.  The download requester
opens, but it does not have my preferred viewer entered as the choice to open
the file with.  Very inconvenient to always click through my directories to
choose my viewer app ...

2.  If the email comes from Mozilla (e.g. if I send it from one of my accounts
to the other), clicking on the attached JPEG image causes Mozilla to display the
image in the browser window.  Even more inconvenient - it actually loaded an
image over this bug report, when I was testing again while writing my report!  
Please note that I have also unchecked JPEG images in Preferences/Advanced/System
because I do not want Mozilla to handle these.

On the other hand, when I receive Excel (.xls) files which have no MIME type and
are also recognized as an "application/octet-stream" Mozilla conveniently
suggests to open them with soffice6 (OpenOffice 1.01) in the download window.
When I receive Word files (.doc) which Mozilla recognizes as "application/word"
MIME types, and also suggests to open them with soffice6, although I have no
helper application defined for this MIME type.  

I have, however, set the default application for both file types in my Windows
Folder options to soffice6, so this actually works fine from within Mozilla.  It
should be noted that it even works with the .xls file which has no MIME type,
not even under the windows folder options.

On the other hand, .jpg images are also set to be handled by my default viewer
app in windows folder options, and they are not handled at all in the way I want
them to be handled.

Last not least, PDF files seems to work generally (I have defined the helper app
and MIME type here), whether they are mailed by Mozilla, a different mailer, or
found as a link on a website (I have deactivated the Acrobat plugin since I do
not want to open the Acrobat Reader inside the Mozilla window).

I would suggest that Mozilla handles email file attachments which have unknown
or known MIME extensions generally in the following order:

1. If a helper application for the MIME type is defined, suggest this helper app
to open the file with.
2. If the MIME type is "application/octet-stream" but the file extension matches
that of a MIME type for which a helper application is set, suggest this helper
app to open the file with.
3. If no helper application is defined for a MIME type, which is however
recognized by Mozilla, suggest the application which is set as default for this
MIME type in the windows folder options.
4. If the MIME type is "application/octet-stream" and there is no helper
application specified that uses this file extension, suggest the application
which is set as default for this file extension in the windows folder options.
5.  If none of the above, there is probably nothing to suggest by default....

I actually think this this is a problem that causes major inconveniences, and
hope someone can have a close look at it soon ...


16 years ago
Target Milestone: --- → mozilla1.1beta
> 2. If the MIME type is "application/octet-stream" but the file extension matches
> that of a MIME type for which a helper application is set, suggest this helper
> app to open the file with.

That is _exactly_ what should be happening.  What version of Mozilla are you
using?  Do you have application/octet-stream listed in helper app preferences?
Target Milestone: mozilla1.1beta → ---

Comment 2

16 years ago
I have been using Mozilla 1.1 beta, and since today Mozilla 1.1
(Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.1) Gecko/20020826)

I don't have application/octet-stream defined in my helper apps, because these
might be any unknown file format, and I am happy that e.g. Excel files who come
as application/octet-stream MIME types are recognized by their .xls extension,
and Mozilla suggest soffice6 (Open Office) to open the file, as I have set it in
my systems folder options->file types.

I have however defined a MIME type for image/jpeg  for all files with extensions
.jpg, .jprg, .jpe . But Mozilla does not recognize these extensions when
attached JPEG images come as application/octet-stream MIME types, and does not
suggest the helper application (IrfanView) I have defined for the image/jpeg
MIME type.  Irfan view is also set as my systems default application for .jpeg
files in folder options->file types.

Comment 3

16 years ago
I'm having the same inconsistency in Mozilla running on Macintosh,  if I set up 
a file extension and MIME type with the extension mapped to the software I need 
to use,  and a mail attachment of that type arrives, Mozilla doesn't recognizes 
the MIME type I defined on the Preferences/Helper Applications,  it also 
bypasses the MIME/extension configuration of the operating system.  It just 
shows a "application/octet-stream".

This problem is stoping the deployment of Mozilla as the main browser in my 

Comment 4

16 years ago
This bug should be changed to ALL OS, my problem is with Mozilla 1.1 on Mac OS 
and Windows 2000


16 years ago
QA Contact: trix → yulian
QA Contact: yulian → stephend
ok, this is just a bug in the way we pull the MIME info for types we handle

*** This bug has been marked as a duplicate of 58554 ***
Last Resolved: 16 years ago
Resolution: --- → DUPLICATE
verified dup
Product: MailNews → Core
Product: Core → MailNews Core
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