Live Data Font Awesome sort icons disappear for small columns or with FA7 in Firefox

Steps to reproduce:

1. Make sure the wiki uses Font Awesome as icon theme
2. Open any Live Data like the Wiki Index
3. Resize the currently sorted column (by default, the Name) until the full column name isn't visible anymore

Expected result:

The sorting arrow is still visible to show the column that is sorted.

Actual result:

The sorting arrow isn't visible anymore.

This is a regression compared to 15.10.16, i.e., before XWIKI-21009. In XWiki 18.0.0RC1 the regression becomes worse, with Font Awesome 7 in Firefox but not in Chrome, the sorting icons aren't displayed at all anymore, instead an ellipsis (…) is displayed.