1495197 - With identical HTTP response headers, extension in the URL changes behavior

Status: RESOLVED INVALID

(Firefox :: Untriaged, defect)

Description

[Thanassis Tsiodras]

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:62.0) Gecko/20100101 Firefox/62.0
Build ID: 20180920131237

Steps to reproduce:

After mirroring a website locally and serving it from a local nginx installation, I tried opening one of the URLs:

    https://ttsiodras.verymad.net/Eli.Bendersky/tag/serial-port




Actual results:

Firefox 62.0.2 replied with "You have chosen to open BIN file" and offered to save the content...



Expected results:

The response is of content-type/html - Firefox should have just displayed the content (as e.g. Chrome does), not offer to save it. 

Adding a symlink with an .html extension that points to the same file proves that this is valid HTML content - and Firefox shows this just fine:

    https://ttsiodras.verymad.net/Eli.Bendersky/tag/serial-port.html

Note that both URLs in fact return the exact same response - including response headers:

    $ curl -I https://ttsiodras.verymad.net/Eli.Bendersky/tag/serial-port.html
    HTTP/1.1 200 OK
    Server: nginx
    Date: Sat, 29 Sep 2018 11:11:13 GMT
    Content-Type: text/html
    Content-Length: 5443
    Last-Modified: Sat, 29 Sep 2018 10:36:17 GMT
    Connection: keep-alive
    ETag: "5baf55a1-1543"
    Accept-Ranges: bytes

    $ curl -I https://ttsiodras.verymad.net/Eli.Bendersky/tag/serial-port
    HTTP/1.1 200 OK
    Server: nginx
    Date: Sat, 29 Sep 2018 11:11:15 GMT
    Content-Type: text/html
    Content-Length: 5443
    Last-Modified: Sat, 29 Sep 2018 10:36:17 GMT
    Connection: keep-alive
    ETag: "5baf55a1-1543"
    Accept-Ranges: bytes

Why would Firefox be looking at the "file extension" instead of the content type to decide whether to render or save the content?

Comment 1

[Thanassis Tsiodras]

My bad - I had to clear the browser cache (it had stored a previous content-type).