Reported in pairing session with Amir.

Steps to reproduce:

Scenario: Enabling fonts downloading without saving the preferences
Given I am logged in
And I have reset my preferences
And I set "German" as the interface language
And I open ULS
And I open Display panel of language settings
When I open Fonts panel of language settings
When I click the checkbox to enable fonts downloading
And I select OpenDyslexic font for the content language for the live preview
And I close the panel to discard the changes
And I open Display panel of language settings
Then a font selector for interface language doesn't appear
And a font selector for content language doesn't appear
And the active interface font must be the same as font prior to the preview
And the active content font must be the same as font prior to the preview

It seems that, this is Live Preview bug, #56081

Upstream fix: https://github.com/wikimedia/jquery.webfonts/pull/41

Change 118977 had a related patch set uploaded by Amire80:
WIP: Update webfonts from upstream

https://gerrit.wikimedia.org/r/118977

Change 118977 merged by jenkins-bot:
Update jquery.webfonts from upstream

https://gerrit.wikimedia.org/r/118977