Browser caching does not work with range request set for Firefox

Dear PDF.JS contributors,

When range requests are set and http server configured to cache contents with public, max-age=31536000, immutable, browser caching does not work on Firefox but strangely it works on Chrome or Safari.

Attach (recommended) or Link to PDF file here: not file specific, but one can use https://public.fays.io/public/c80f5905-e4aa-4df3-8fa8-ab2dd3d04320.pdf

The server configuration is:

Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: GET, HEAD, PUT, POST
Access-Control-Expose-Headers: Accept-Ranges, Content-Range, Content-Length, x-amz-request-id, x-amz-id-2, ETag
Access-Control-Max-Age: 31536000
Vary: Origin, Access-Control-Request-Headers, Access-Control-Request-Method
Cache-Control: public, max-age=31536000, immutable

Configuration:

Web browser and its version: Firefox 73.0
Operating system and its version: mac os x 10.15.3 
PDF.js version: 2.2.228
Is a browser extension: no

Steps to reproduce the problem:

1. clear the browser cache
2. go to https://app.fays.io/fd7be64d-ec78-4731-9dff-7b9c8088acf9 and open the developper tool
3. refresh the page, the range request works fine but they are not cached by Firefox (private browser cache: https://developer.mozilla.org/en-US/docs/Web/HTTP/Caching)

What is the expected behavior?

On Chrome, when one refreshes the page, the range requests have been cached. A page refresh leads to:

What went wrong?

On Firefox, the range requests are not cached by the private browser cache. Also, Firefox performs in this example a 1.2MB download because the first range request has Range: bytes=1577535- and the response header has a code 206.

On the other hand, PDF.JS on Chrome requests bytes=0-262143 and the response header has a code 200.

I don’t know why it behaves differently.

**Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension): ** https://app.fays.io/fd7be64d-ec78-4731-9dff-7b9c8088acf9

Best, A.

[Snuffleupagus]

Given that caching is controlled by the browser itself, I’m not really sure that this is actually an actionable bug for the PDF.js library. If anything, it sounds more like a (possibly general) bug in Firefox and I’d thus suggest reporting it in Bugzilla instead.

[Snuffleupagus]

When opening an issue, please provide all of the information requested in https://github.com/mozilla/pdf.js/blob/master/.github/ISSUE_TEMPLATE.md

Furthermore, the likelihood that someone will assist you is a lot greater with a small and self-contained example (rather than a larger viewer); please see https://github.com/mozilla/pdf.js/blob/master/.github/CONTRIBUTING.md (emphasis mine):

If you are developing a custom solution, first check the examples at https://github.com/mozilla/pdf.js#learning and search existing issues. If this does not help, please prepare a short well-documented example that demonstrates the problem and make it accessible online on your website, JS Bin, GitHub, etc. before opening a new issue or contacting us on the IRC channel