Just compare these two screenshots of mine:

https://prnt.sc/1tcg6o2 - firefox 

https://prnt.sc/1tcg5q2 - chrome

 

What's up with the white bar at the top?

thats not broken aero at all
they just made the bar filled with more white layer

you still have glass and blur ...

this is probably them trying to "follow" windows 11 look (aka frosted glass), which shouldn't surprise you by now...
 

also this effect is actually nothing new either, it was there ever since they went to Australis "UI"
and that one is old ...
you get it if your tab bar isn't skinned; like so:

 

Edited September 23, 20214 yr by vinifera

This Aero theme is the closest you'll get to the look of how you could get Firefox to look in the golden age from around 2009 or so. This isn't mentioned, but you must also turn on toolkit.legacyUserProfileCustomizations.stylesheets in about:config page, the chrome folder in the ZIP goes to your profile folder, check it on about:support page.

I haven't looked into what exactly is needed if you only want proper aero in the upper area.

This method doesn't restore rendering of plain web page elements, like buttons, radio boxes, check boxes scroll bars etc. These rendered using OS theme in the old versions, apparently there's still a pref to restore them that way by disabling widget.non-native-theme.enabled and enabling widget.disable-dark-scrollbar.

Setting browser.uidensity to 1 will enable compact mode, which reduces URL/search bar height.

Edited November 13, 20214 yr by UCyborg
Additions I didn't know about at first

There is a way to remove the white layer at the top - just add the following to userChrome.css:

#TabsToolbar {
  background-color: transparent !important;
  background-image: none !important;
}

 

On 9/23/2021 at 5:08 PM, Jaguarek62 said:

Just compare these two screenshots of mine:

https://prnt.sc/1tcg6o2 - firefox 

https://prnt.sc/1tcg5q2 - chrome

 

What's up with the white bar at the top?

They had already done something similar like this with Windows Vista, where they broke the Aero Theme in Chrome with v42 (?). I think it shows that they do no longer care so much in developing for that OS anymore. They also ended support for Windows Vista a few versions later. Windows 7 will probably be shifted to ESR soon with version 102