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When downloading from Outlook on the web using Firefox ESR, an unnecessary string is added to the file name.

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When accessing Outlook (https://outlook.office.com) using Firefox ESR version 128.9.0 and attempting to download a file attached to an email, the string 'UTF-8' is automatically inserted at the beginning of the file name, which is causing issues. This phenomenon does not occur with other browsers such as Edge or Chrome.

Is there a way to solve this problem?

When accessing Outlook (https://outlook.office.com) using Firefox ESR version 128.9.0 and attempting to download a file attached to an email, the string 'UTF-8' is automatically inserted at the beginning of the file name, which is causing issues. This phenomenon does not occur with other browsers such as Edge or Chrome. Is there a way to solve this problem?

Wybrane rozwiązanie

I'm looking at this in Firefox 137.0.2. For a file named

Voucher - MAIKOYA.PDF

Firefox shows that the server is sending this header:

content-disposition: attachment; filename*=UTF-8''Voucher%20-%20MAIKOYA.pdf

Now, that seems a bit weird, compared to the usual format --

content-disposition: attachment; filename="Voucher - MAIKOYA.pdf"

-- but the MDN article on Content-Disposition implies that this is one of the normal options, so Firefox should know how to handle it. https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Content-Disposition#syntax

Since I can't tell whether Microsoft is doing anything at odds with the web standard, I filed a new bug:

https://bugzilla.mozilla.org/show_bug.cgi?id=1961710

If you want, you can add yourself to the CC list and keep an eye on whether they ask for more testing.

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Wybrane rozwiązanie

I'm looking at this in Firefox 137.0.2. For a file named

Voucher - MAIKOYA.PDF

Firefox shows that the server is sending this header:

content-disposition: attachment; filename*=UTF-8''Voucher%20-%20MAIKOYA.pdf

Now, that seems a bit weird, compared to the usual format --

content-disposition: attachment; filename="Voucher - MAIKOYA.pdf"

-- but the MDN article on Content-Disposition implies that this is one of the normal options, so Firefox should know how to handle it. https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Content-Disposition#syntax

Since I can't tell whether Microsoft is doing anything at odds with the web standard, I filed a new bug:

https://bugzilla.mozilla.org/show_bug.cgi?id=1961710

If you want, you can add yourself to the CC list and keep an eye on whether they ask for more testing.

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Thank you, jscher2000. I have gained a better understanding of this issue. I will also keep an eye on the progress of the bug report. I will close this question now.

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In follow-up searching, I saw reports that Safari also doesn't understand the new Content-Disposition headers from Outlook. Even if Microsoft doesn't care about Firefox users, maybe they'll roll it back to reduce the impact on Safari users. Fingers crossed.