The toolbar item that showed if the current page was loading was removed in Australis. By popular request, see credits, this addon was created to restore this feature.
Details on Using Custom Images
From the options page in the Add-on Manager tab, you can select custom images to use for the loading or idle throbber. In the file picker that opens you can copy and paste a link, or browse to and pick any file on your computer. A copy of the file is made in the add-on, so you can delete the image from your computer and it will still work. On uninstall of the add-on the copy of the images are deleted. The copy of the images can be found in your profile folder and are named "throbber-restored-customImageLoading" and "throbber-restored-customImageIdle".
If you used a custom image "A" for loading, a file in the profile directory named "throbber-restored-customImageLoading" will be created. Then later decide to use custom image "B" for loading, this same file will be overwritten.
Addon Compatability Issues for v1.0 and v1.1 with "Classic Theme Restorer"
Thanks to Omahaa100 for the solution to this problem. This affects v1.0 and v1.1.
by Omahh100 on May 19, 201
I tried using this add-on AFTER I had already added "Classic Theme Restorer" for FF 29. Much like "No luck at all" it didn't show up anywhere! I tried restarting....nothing. So I disabled CTR and restarted again and the throbber was right there on my navigation bar! Then I re-enabled CTR and now they're both working fine :)