Reproduce:

1. Open Firefox
2. Log in to your account
3. Open preferences
4. When you scroll down the "Save, restore all default settings (in all sections)" is floating while scrolling down, sometimes it hides the setting names, especially when you

*hold down the left button on mouse while scrolling down.
*hold down the middle button (if you have) on mouse while scrolling down.

How it should work:
*Like on Google Chrome, the save bar stays on bottom all the time and not moving while scrolling the page.