The new top bar adjusts to the window size instead of clipping important stuff off to the right in smaller viewports. However, on sites with the new responsive design, individual pages that aren't yet responsive now clip the top bar. This is a screen shot from my Meta.SE profile in Firefox 60.0.1 on Windows 7 in a window that's currently 1036px wide:
Here's another site for comparison:
The "ask question" page is one of the ones that's not responsive, by the way, so I had to side-scroll to get to the site switchers to get the second screen shot.
I know that eventually everything will be responsive, but that's going to take a while. In the meantime the top bar has regressed. Can we fix that?
A comment asked about zoom. I reproduced it at 100% zoom and then zoomed out a few more notches for good measure. Zoom does not affect the layout of the top-bar icons: