The Ubiquity installer slideshow displays Firefox with a custom icon. This presents two problems:
- It's not the icon that the user will actually see on the system, which is a usability issue (and it's also inconsistent; all the other icons shown in the slideshow match what the user will see after installation)
- Using a custom icon violates Mozilla's guidelines (see https://design.firefox.com/photon/visuals/product-identity-assets.html)
We should use Firefox's standard icon in the slideshow.
