Google Accounts is quite different from Firefox Accounts, regarding the Sync service.

You can't access data while it is on the Sync servers, that wasn't a design parameter. Your data is encrypted before that data is uploaded to the Sync service and de-crypted as your data comes to each device. No one can access your data while that data is in-transit or while it is on the Sync servers. And there is no "management" features provided, short of what is in Options > Sync on each device for what types of data is sync'd to and from each device.

Sync was built to be automatic once it is set up and remains enabled, so the user doesn't need to do anything beyond setting it up and using Firefox.

Thanks, I think it would be a useful feature though.. Is there a change we might see this in the future?

Truthfully, I doubt it without lessening security for user data.

Encryption for password data is too important to allow for web access, which would also make it possible for that data to be accessed by server maintenance personnel or Mozilla staff. Plus, it make easier to "hack" that data from the internet. Currently the encryption "key" is held on the users devices - no one else has access to it.

The encryption key as was used in the previous version of Sync was a ponderous 26 character alpha/numeric string that too few users saved [as advised on the final setup panel when they initiated Sync]; now it is "hidden" implementation and not user-facing. A major improvement that I have "seen" in Sync support questions here since last April when the new Sync came out in Firefox 29.

Overall IMO, data like bookmarks really doesn't need to be encrypted, and maybe the same for browsing history, but that require a "mind set" change by the Mozilla developers. Two separate streams of data; one encrypted and one not, relying solely on the HTTPS connection to the Sync servers.

I am curious what types of data that you would want to be able to be able to access from the web?

In the past I have used my personal web space with Comcast to have a page with my bookmarks, so I could access them from any computer anywhere, that allowed full internet access. I also used to carry a USB Key with Firefox Portable installed (and Sync'd with my main desktop PC) so I could use my own Firefox on any Windows PC that allowed a USB Key to be plugged in and accessed. Major corporate intranets usually don't allow that.