Every sample is followed by a screenshot of the correct behaviour as seen in Firefox 3.6.12 on Mac OS X.

  1. A required ligature must be kept when the letter-spacing is increased:

    Benutzer – Benutzer

    correct Firefox 3.6.12 display of “Benutzer”

  2. When a ZWJ is used to force a required ligature, there should be no space when letterspacing is increased:

    ſchlieſ‍zen – ſchlieſ‍zen

    correct Firefox 3.6.12 display of “schließen”

  3. Other ligatures must not be kept when letter-spacing is increased:

    Etikett – Etikett

    correct Firefox 3.6.12 display of “Etikett”

  4. When an ZWNJ is used to inhibit a required ligature, there should be no additional space when letterspacing is increased:

    Zeit‌zone – Zeit‌zone

    correct Firefox 3.6.12 display of “Zeitzone”