Adblock Plus 3.3.1 on Firefox 60.3.0esr
OpenSuse Leap 15
Thought at first Firefox bug, opened this issue: https://bugzilla.mozilla.org/show_bug.cgi?id=1501832
As you may read, incorrect page display (screenshots appended to bug report) is triggered by Adblock Plus. Although no blocked ads on page, internal router admin pages.
Page is displayed correctly as long as Adblock Plus is disabled. "Disabled on page" with active Adblock Plus is not enough.
Workaround, of course: Temporarily disable Adblock Plus when setting up router.
