The container grows, and I saw a realtor having more than 40 containers because each client have their account.
I don't have that much but the longer I work/study/family bother me with technical help. I had the need to create more Containers.
I suggest, to be able to create folders to Organize containers and assign different color to each folder (not a limited set of colors)
Also to add Separators like how you can in Firefox's bookmark pages. it is a nice feature.
Thanks for submitting an idea to the Mozilla Connect community! Your idea is now open to votes (aka kudos) and comments.