Why different ViewPort sizes in Chrome and Firefox?

Question

JavaScript

I'm trying to take a screenshot in Goole Chrome via the Chrome.Tab API - captureVisibleTab.
I look at the parameters of the visible part of the image

>screen
Screen {availWidth: 1438, availHeight: 1150, width: 1436, height: 1149, colorDepth: 24, …}
availHeight: 1150
availLeft: 1437
availTop: 0
availWidth: 1438
colorDepth: 24
height: 1149
orientation: ScreenOrientation {angle: 0, type: 'landscape-primary', onchange: null}
pixelDepth: 24
width: 1436
: Screen

I see the same thing in Firefox:

>screen
Screen { availWidth: 1280, availHeight: 1024, width: 1280, height: 1024, colorDepth: 24, pixelDepth: 24, top: 0, left: 0, availTop: 0, availLeft: 0 }

Slightly goofing off and trying to google.
Interestingly, in Chrome captureVisibleTab gives a picture with real screen dimensions - 1281 x 1046. I did not try to capture the screen in Firefox.

And the question is: how to find out the real dimensions of the ViewPort in Chrome?
document.documentElement.clientHeight and document.documentElement.clientWidth are not real values!

Chrome 98.0.4758.102
Firefox 97.0 (64 bits)
OS Ubuntu 18.04 with Mate Desktop.
Desktop on two monitors

ps: after rebooting the system, chrome determined the correct dimensions of the ViewPort! It's still not clear, because with an incorrectly defined ViewPort, all sites were displayed without distortion.

Answer 1

availHeight is css pixels , which are indirectly related to real ones. Try zooming in the developer console and sipping the screen border while changing the resolution. There will also not be real numbers)
but about .documentElement.clientHeight
documentation on MDN

Answer 2

In short, Chrome for some reason incorrectly determines the display settings.
Left mate for cinamon. In cinamon, while the parameters are determined by Chrome correctly.