Hello, everyone!
I have found that if window width in range 760-777, header menu don`t visible.

In other cases it looks like this:

or like dropdown

I can't find this problem anywhere on the site. Could you provide a URL or steps to reproduce this?
@georgegillams here

Good catch!
This seems to be specific to the mozilla.org/ru (which uses a slightly different style of menu to other versions).
Will take a look tomorrow if someone else doesn't beat me to it 👍
I believe this is bug https://bugzilla.mozilla.org/show_bug.cgi?id=1401978
@alexgibson it is similar, but in this case it is range (760-777) not the one pixel
@alexgibson it is similar, but in this case it is range (760-777) not the one pixel
I just tested this in responsive design mode on the German home page: https://www.mozilla.org/de/
Only at exactly 760px does the nav disappear. It reappears for me at 761px
@sweatC the behaviour seems exactly the same on de as on ru. See gif below - the menu is only missing at that exact width

I agree, It is kind confusing thing because I have tested it using _google chrome browser_, so when
I have launched it on firefox it looks like in your gif above.
All I'm trying to say is this:
The issue you've seen on https://www.mozilla.org/ru is the same one as https://bugzilla.mozilla.org/show_bug.cgi?id=1401978 describes on https://www.mozilla.org/de
I hope the screenshots below help to clarify this:

@georgegillams Did you try to test your website using Google Chrome?
To try and save some back and forth here, this bug will be present in the header on any page, for every non English locale.
The issue is also only evident at 760px in Google Chrome (the website uses the same breakpoints, regardless of the browser). @georgegillams is correct that this is the same bug as the one I linked to earlier.
@sweatC yes I did
Glad we got to the bottom of this. For future issues, it's useful to include what OS / browser you are using, and the URL / steps to reproduce.
😎
@georgegillams I got it 😅
I didn't find this sort of problem on the site.
Can you just send me Url? @sweatC
@pandyamarut you are welcome