Twitter – How to remove a Twitter avatar and reset it to default

The problem has been solved per se after I have cleared the history and removed all cookies from Firefox.

1. Click your name or existing profile photo at the upper left corner of the screen to go into your profile.
2. Once there, the third or so item under your big profile pic at upper left should be "Photos". Click on this.
3. Click on your "Profile Pictures" album.
4. Click on the photo you want to use as your profile picture. It will expand into the centre of the screen with a bunch of stuff on the right.
5. In the upper right corner there are three icons, a gear, a downward arrowhead, and an X. Click the gear icon.
6. A drop-down menu will appear. The second-last item on the menu should be "Make Profile Picture". Click on this.

After a few seconds you will be back at your profile screen, with the selected picture as your profile picture.