Media observable is not triggering in Firefox print preview

[aciccarello]

Bug:

The media observable is not firing for a custom breakpoint in the Firefox print preview.

What is the expected behavior?

When printing, both Chrome and Firefox should be updated by the media observable.

What is the current behavior?

Chrome is updating on the media observable while Firefox is not.

What are the steps to reproduce?

View this StackBlitz and open a print preview (it's best to open the app in another page). Chrome will show "Print: true" while Firefox will show "Print: false" indicating that the media query did not update the print view.

What is the use-case or motivation for changing an existing behavior?

The media observable should function the same across browsers. Print media is an example of custom breakpoints in the library.

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

Angular 5.1.1
Chrome Version 66.0.3346.0 (Official Build) canary (64-bit)
Firefox 58.0.1 (64-bit)
Windows 7 64-bit

Is there anything else we should know?

[CaerusKaru]

I'm going to say that this is not a bug with our implementation, and likely a bug with the Firefox implementation. One of two things is probably happening: 1) Firefox doesn't fire the print event in time for the print preview dialog to be rendered (likely), 2) there's a bug preventing matchMedia from picking up print events (unlikely).

In either case, this isn't a bug with our library. Unless there's evidence provided to the contrary, I'm closing this issue. We can reopen if evidence is given.

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