Removing The Throbber
Removes the Throbber from the toolbar

---

Tweak Type:	Display
Fx 2:	YES
Fx 3:	YES
Fx 3.5:	YES

For those looking to get even more space on their toolbar or simply don’t care for the Firefox Throbber, here is an easy way to remove it.
Note: you will need the ChromEdit Plus extension

1. From Firefox Tools Menu Select ChromEdit Plus then ChromEdit from the submenu or click the ChromEdit button
2. Scroll to the bottom of the document
3. Copy and paste the following:
   
   #throbber-box {
   display: none !important;
   }
4. Click the ‘Restart Firefox’ button.
5. The Throbber will be gone after the restart

Source