As an addition to joshnh answer, if anyone has the same issue:
Watch out: text-align: justify;
needs a space after every display: inline-block;
element to work. Otherwise the elements are treated as one word and will not distribute horizontally.
So this won't work:
<!-- HTML -->
<ul><li>Item 1<li><li>Item 2<li><li>Item 3<li><li>Item 4<li></ul>
But this will:
<!-- HTML -->
<ul>
<li>Item 1<li>
<li>Item 2<li>
<li>Item 3<li>
<li>Item 4<li>
</ul>
I just had this issue because we are minifying our HTML-Markup and the minifier puts everything in one line.