CSS issues on User Groups page in Firefox

Steps to reproduce:

1. Login to Forum as User with Administrator permissions.
2. Go to Administration -> User Groups page.
3. Hover the cursor up and down over the first row of User Groups table and table header row
4. Overview the text inside table rows while hovering

Actual results All text inside the table rows is jumping up and down on few pixels.
Expected results No changes in text position inside the table rows should be made