This happened to me as well. I am a Mac user. I deleted the icon from my dock, went to applications and dragged firefox back down and the normal icon is back. hope this helps!

I actually did the same thing when I couldn't Find another solution. Thanks for the reply.

Am on a Mac as well. I right-clicked on the icon in the dock, and chose "options" from the drop-down menu.

From within the options menu I chose "keep in dock" and it changed from the "pencils/paper" icon to the "globe" icon.

I'm reading all the problems for Mac in the support groups and I must say I'm not inclined to update. It seems there are more problems than solutions.