synthesizeNativePointer (https://searchfox.org/mozilla-central/rev/be906232eedb22c064b78f3806b38964c04f1fbc/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/PanZoomController.java#741) doesn't convert clientX and clientY to right coordinates. I guess that we may have to use getClientToScreenMatrix or getClientToSurfaceMatrix to post right mouse point on mouse event.

https://treeherder.mozilla.org/jobs?repo=try&revision=3018fc230f5513c0823a8f9dbfd7b73cabbdd6d8

Hmm, we should use right screen coordinates on SendNativeMouseEvent.

https://treeherder.mozilla.org/#/jobs?repo=try&revision=65e522233eea7415ebe229e7e95b419353e980d9

One is screen coordinate issue (bug 1701546). another one is GeckoView's mouse button emulation of SynthesizeNativeMouseEvent.

Button state is current button push state. So when on ButtonUp, this is 0.

We have to consider mobile viewport scale to calculate screen position.
And mozInnerScreen isn't valid position if that scale isn't 1 (bug 1701546).

Also, this function won't work on Fission+xorigin with mobile viewport due to
no way to get current mobile viewport scale since window.top isn't same
origin.

Depends on D110197

This test is often failure on debug build due to zoom to focused input.

Depends on D110198

https://hg.mozilla.org/mozilla-central/rev/482fec13b96f
https://hg.mozilla.org/mozilla-central/rev/5735e7f86a01
https://hg.mozilla.org/mozilla-central/rev/72ff67f96a3f

From https://searchfox.org/mozilla-central/rev/ae02905b1c4e7c2e6f974a3cfad24503006110ac/testing/mochitest/tests/SimpleTest/EventUtils.js#1108-1114

  let resolution = 1.0;
  try {
    resolution = _getDOMWindowUtils(win.top).getResolution();
  } catch (e) {
    // XXX How to get mobile viewport scale on Fission+xorigin since
    //     window.top access isn't allowed due to cross-origin?
  }

You can just use SpecialPowers.spawn;

  const resolution = await SpecialPowers.spawn(window.top, [], () => {                
    return SpecialPowers.getDOMWindowUtils(content.window).getResolution();     
  });