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Firefox ignores response header Content-Type

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I have a configured nginx server returning the following headers when serving plain, non-UTF encoded text files.

Content-Type: text/plain; charset=ISO-8859-1 Content-Disposition: inline

When the text files contain ANSI escape sequences (Standard ECMA-48) Firefox will often ignore the server Content headers to use a guess determined by the file extension. But the guess is often wrong and forces the browser to download the file instead of displaying it in the tab.

Cause: document Type: application/x-vnd.mozilla.guess-from-ext; charset=ISO-8859-1

Is this intended behavior and is there anything else I can do to encourage Firefox to display the text file in a browser tab? As this is not the same behavior with other browser engines such as Blink or Trident.

6 sample files, all refuse to display in Firefox except 'r5-WTF4.ans' https://retrotxt.com/e/

I have a configured nginx server returning the following headers when serving plain, non-UTF encoded text files. Content-Type: text/plain; charset=ISO-8859-1 Content-Disposition: inline When the text files contain ANSI escape sequences (Standard ECMA-48) Firefox will often ignore the server Content headers to use a guess determined by the file extension. But the guess is often wrong and forces the browser to download the file instead of displaying it in the tab. Cause: document Type: application/x-vnd.mozilla.guess-from-ext; charset=ISO-8859-1 Is this intended behavior and is there anything else I can do to encourage Firefox to display the text file in a browser tab? As this is not the same behavior with other browser engines such as Blink or Trident. 6 sample files, all refuse to display in Firefox except 'r5-WTF4.ans' https://retrotxt.com/e/
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cor-el said

See:

Hi thanks, but it seems with Firefox nosniff only works with script or css, but not text/plain.

Note: nosniff only applies to "script" and "style" types.

nosniff

   Blocks a request if the requested type is
       "style" and the MIME type is not "text/css", or
       "script" and the MIME type is not a JavaScript MIME type.