currently you can only view synced history items for current devices. What I request is to view history items from all synced devices.

It's even more restricted than that, unfortunately...we only sync the last 30 days of history when you connect a new device (though Firefox for iOS will backfill your full history), only the 20 most recent visits for each page, and prune old pages after 60 days (they'll remain on any existing synced devices, but new devices that you connect won't have your full history). We also don't store the device origin (bug 1302797), so bucketing history based on where you visited the page isn't possible. We've known about the limitations (see bug 1157553, comment 6, for example) of history sync for a while (though I can't find a meta bug for it! :-) So let's use this one), but redoing it is a substantial chunk of work that we're unlikely to get to in the near future. However, having a single Sync implementation for all our projects (what we're working on now, over in https://github.com/mozilla/application-services) will make it much easier to make changes like this. Thanks for filing!