[WIP] nav tweaks

* [x] https://bugzilla.mozilla.org/show_bug.cgi?id=1096654
* [x] https://bugzilla.mozilla.org/show_bug.cgi?id=1083627
* [x] https://bugzilla.mozilla.org/show_bug.cgi?id=1084016 (needs works at mobile width)
* [ ] https://bugzilla.mozilla.org/show_bug.cgi?id=1059002 (scroll stuff needs work)

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# do not merge