midsize browser window jumbles xfinity.com display

@XfinityKei​, thank you for looking at this so promptly!

I just now looked at xfinity.com on Chrome (which I almost never use), and the problem is not there. The site switches from neat links across the top to a hamburger menu at a certain width, no fuss, no muss.

I'm seeing this problem in Firefox 158.0.1, on Windows 11 25H2, build 26200.9457, but I updated both Firefox and Windows in the last week. I was seeing this issue before those updates as well.

Unfortunately, the whole interface for phone apps is very difficult for me to use. Not a realistic option in my particular case.

@user_y7rb33 Is it multiple sites or just one site with the issue?

Did the issue start after you updated your browsers?

@XfinityKei​, do please read carefully. You've run into a long-time English major here.    8^p    (That's an old-fashioned text emoji. Look at it sideways.)
As I said in my previous response, I updated both Firefox and Windows in the last week. >>I was seeing this issue before those updates as well.<<

I haven't seen the problem on any site other than xfinity.com. The problem appears on every page I've seen in xfinity.com where those nav links are across the top. As you probably know already, the site is painfully slow, but I did take the time just now to:
= verify that the problem appears at xfinity.com;
= verify that the problem appears at https://customer.xfinity.com/membership;
= shut down Firefox and restart it (which did another update, so now I'm running Firefox 159.0 (64-bit));
= re-verify that the problem appears at xfinity.com;
= re-verify that the problem appears at https://customer.xfinity.com/membership.
So that makes at least two Windows 11 releases and at least three Firefox releases where this problem appears.

Thank you for persisting in figuring this out!

@XfinityPeterH​ The problem appears at 100% zoom and 90% zoom. It no longer appears at 110% or 80%.

If I set the zoom to 90% and start widening the window, the nav links snap back into position while the window is still a good bit narrower than if I do the same at 100%. Predictably, if I *narrow* the window at 100%, the hamburger menu appears while the window is still a good bit wider than if I do the same at 90%.

(In my thoroughly amateur analysis, all this suggests we're looking at a CSS pixels issue.)

@XfinityMichaelC​ Sorry <sigh>. It still happens in a brand-new Private Window:

ps: Thanks, y'all, for staying on this! I've been retired from IT work (though I was never a coder) for a couple years now, and it's fun to do this stuff again (for a little while)!

As my testing brain comes somewhat back on line, it occurs to me that I tend to customize my interfaces a great deal.
So I turned off my Firefox theme and refreshed the page. No change.

Turn off UBlock? No change.
And of course we already tried a Private Window.

Other customization tools I'm using include:
Open-Shell 4.4.198
ESET Security 19.2.10.0
Power Toys (Preview) x64 0.96.1
Winaero Tweaker 1.65.0.0
Windhawk v1.6
WinSetView 3.1.7
But I no longer remember exactly which abilities of these I'm using, so I hesitate to shut them down and possibly lose my settings in them.