http2-server-push | WordPress plugin that enables HTTP | Content Management System library

So there can be a few things after some testing with various configurations, browser versions and flags enabled/disabled within Chrome as well as investigating with the network event viewer.

If the LiteSpeed Web Server has QUIC enabled, Chrome v71 seems to be showing the request as a normal GET request, and won't indicate it being pushed, however looking in the network event viewer in Chrome, it reveals that it indeed is pushed (Look for QUIC_SESSION_PUSH_PROMISE_RECEIVED).

Now, this will only be the case if QUIC in the browser is enabled as well, which it isn't by default currently in Chrome v71 as far as I can tell (they disable and enable things from time to time) - so you either have to have a flag set in Chrome to enable QUIC and you'll see the above behavior (You should also see http/2+quic/43 in "Protocol" under web developer tools).

If QUIC isn't enabled in the Browser or on the web server, you should see the file being pushed, and Chrome v71 would indicate this with the Initiator "Push / Other".

Now, in Chrome v73 (Canary release), it will have the "Initiator" set to Other and the "Size" should be (from memory cache), this indicates the file being pushed.

In Google Chrome you can go to chrome://net-export/ and click "Start Logging to Disk", then refresh your browser window where you have the file that expects to be pushed - stop the measurement, and go to https://netlog-viewer.appspot.com/ - import the json file here, and go to "QUIC", find your domain name in the list, and click on the "Connection ID".

Then click the "QUIC_SESSION" in the list, and search for QUIC_SESSION_PUSH_PROMISE_RECEIVED - if there's matches, you know for a fact that the files are pushed.

It's a bit of digging to figure out whether it's pushed currently, and the confusion is mainly related to Chrome Dev Tools not really being consistent between protocols and versions.

One way to configure H2 Server Push, is to set the 'Link' header to indicate what resources you want to preload.

You can actually do this through the firebase.json file, like its done for the Polymer HNPWA example: https://github.com/Polymer/hn-polymer-2/blob/master/firebase.json

For instance:

HTTP/2 push only works when the pushed resource is needed by the page (i.e. it's referenced in the HTML). In this case, the fact that /stylepush.css is not loaded by the page at all (never mind by Push as the initiator) shows it is not being used.

If you go to chrome://net-internals/#http2 you should see this as an unclaimed push:

Add a reference to this CSS file in your HTML and you should see it as pushed.

If not, then go to chrome://net-internals/#events&q=type:HTTP2_SESSION in Chrome and provide the HTTP/2 Session data.

Additionally Chrome requires a recognised certificate before it allows you to cache resources (and HTTP/2 resources are pushed into a cache before they are uses). Since Chrome Version 58, they also require the Subject Alternative Name (SAN) to be be set on the certificate, which requires some extra config to set when creating a self-signed certificate.