On an extension page, there's a float:left css for the maintainers field that causes the Used For field to appear in the wrong spot
I mean when clicking through and viewing a given extension from the civicrm.org/extensions directory, e.g. https://civicrm.org/extensions/webform-civicrm-integration
It looks like a field of type entity-reference, and I guess then the outer div gets a class of field--label-inline, which combined with the inner div getting a class of field--items results in the float:left on the inner div.
Doing a css override of
.field--label-inline .field--items { float: none; }
or
.field--label-inline .field--items { float: inherit; }
should fix it.