Link prefetching redownload page in Firefox

StackOverflow https://stackoverflow.com/questions/19997820

  •  30-07-2022
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Question

I'm trying to speed up a Moodle instance (an LMS). I know for certain that users will likely go on their last accessed course, so I'm trying to use link prefetching to download the course page in advance:

<link href='https://moodleexample.io/course/view.php?id=3' rel='prefetch' />
<link href='https://moodleexample.io/course/view.php?id=3' rel='prerender' />

In Chrome, it works rightly. But Firefox shows a strange behaviour. It correctly downloads the web page using prefetch, but when I request the course page, it downloads it again:

Wireshark dump of http requests

You can see from the Wireshark screenshot that it requests the course page again (at time 12.79).

Why does this happen? I tested it on an unencrypted Moodle, and it shows the same unwanted behaviour.

Was it helpful?

Solution

It was Moodle's "fault". They're dynamic pages, so it puts cache headers that block caching of content.

Using the power of Nginx, I rewrote those headers when getting the X-moz: prefetch from Firefox:

if ($http_x_moz ~ ^prefetch$) {
    more_set_headers 'Cache-Control: private, max-age=60'
    more_clear_headers 'Pragma';
}

In the php location. I have also conditionally inserted the prefetch tag only for firefox, using server side browser detection.

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