Greetings,
This is a tiny thing but only recently did I notice it.
On the FF Start page (Desktop version) you offer Top Sites. Use them all the time, love them. If I want to create a custom Top Site, easy -- except when it comes to customizing the image/icon of the Top Site.
For some reason FF insists we store that custom image for that Top Site on the net. If I upload my image somewhere, it doesn't always work properly. Or if I copy a URL of an image I like from the web, sometimes it doesn't quite work either.
Why not, instead -- offer to store the image locally? Firefox is full of folders on our systems. So you'd be offering 'Upload from Desktop' as well as (or perhaps instead of) Custom Image URL.
I hope that made sense.