Firefox doesn't do content sniffing for downloading files AFAIK. What matters to Firefox is what content type the server sends via the HTTP response headers and it is not likely that a server will send a .do file as application/pdf as would be required recognize a PDF file and offer to save it as such.

You can check the HTTP response headers via the network monitor.

• https://developer.mozilla.org/en-US/Tools/Network_Monitor

You can look at this extension created by contributor jscher2000:

• Content-Type Fixer https://addons.mozilla.org/firefox/addon/content-type-fixer/

• /questions/1269057 Viewing document in firefox is all jumbled. How do I fix this?

Hi jcrowingAHHHHHHHHHHHHHHHHHHHHH, this may be a little complicated to work around if the server uses .do on the ends of other types of file names as well (for example, its HTML pages). In that case, Firefox (or an add-on) can't assume that .do = PDF file, it would need to consider other indicia such as the full file name or a Content-Disposition header instructing Firefox to download the file instead of opening it in a tab.

I assumed that the server only sends these PDF files with a .do file extension. If other files are send as well with this file extension then you are out of luck, but if you get a download dialog then I assume that the server sends a generic content type like "application/octet-stream".

Hey everyone, thanks for the replies.

One website in question reports the xmlreport.do file content-type as application/pdf. And yes there are other file types utilised with .do extension, so marking all .do files as pdf's would break the website.

When using Chrome it previews the file in-browser automatically and when you click Save it offers to save the report as xmlreport.do.pdf.

Firefox just comes up with the Save or Open dialog with the file title as xmlreport.do.

We have another site that offers pdf reports as reportitle.html. The header has the content-type set as application/pdf. Chrome displays it as a PDF in-browser; Firefox displays it as html... so you can imagine what it looks like.

It seems Firefox (69.0.1 tested on Win 7 and 10) is ignoring the content-type in the header and going by the file extension; or perhaps favouring the file extension over the header.

cheers

jc

If the file is send as application/pdf then Firefox should open it in a tab in case the builtin PDF Viewer is enabled.

Did you verify this with the Network Monitor or with the Web Console with Network enabled like I suggested above ?

• https://developer.mozilla.org/en-US/Tools/Network_Monitor
• https://developer.mozilla.org/en-US/Tools/Web_Console

If you always get a download dialog then is sounds that you have disabled the PDF Viewer. Make sure you haven't disabled the viewer.

• https://support.mozilla.org/en-US/kb/view-pdf-files-firefox
• https://support.mozilla.org/en-US/kb/disable-built-pdf-viewer-and-use-another-viewer

Via Web Console Network monitor. Here is the reported header:

HTTP/1.1 200 OK Date: Mon, 30 Sep 2019 02:55:05 GMT Server: Apache/2.2.15 (Red Hat) Pragma: No-cache Cache-Control: no-cache,no-store,max-age=0,must-revalidate,proxy-revalidate Expires: 0 Content-Length: 11930 Content-Disposition: :attachment;inline Connection: close Content-Type: application/pdf Content-Language: en-AU

I note the line: Content-Disposition: :attachment;inline

So is Firefox just seeing the attachment parameter and showing the Save dialog? Chrome sees the same header and seems to ignore the attachment parameter and show it inline. Is there an issue with that double full colon?

Firefox's internal PDF viewer is definitely enabled. Other pdf documents show in-browser fine.

cheers

jc

Hi jc, that header value is so wrong. You could try an extension that overrides the "attachment" disposition so Firefox opens the PDF in a tab. I'm not sure that will help with the ultimate problem of Firefox not knowing to suggest a .pdf file extension, but maybe?

I'll suggest mine, since it's so easy to turn on when you need it and off when you don't:

https://addons.mozilla.org/firefox/addon/content-type-fixer/

To turn it on, click the Zzzz button on the toolbar, then click it again to drop its menu and change the Content-Disposition Override setting to "Allow viewing in a tab".

Once you are done overriding, you can change that setting back to "As set by the server" and/or click Stop Listening and Clear Log.

Now, I must confess, I've never tried using it with such a weird header value, so I'm curious what will happen!

See also:

• https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Disposition