This forum might not be the exact right place for this question, but Opensuse is my tribe, so here goes.
I’m using Opensuse V13.2, Mozilla Firefox, Ghostery, everything updated.
When I’m browsing the internets and go to new websites, every once in a while Firefox pauses for about 2-3 minutes, and in the lower left corner of the window, transfering data from s.uicdn.com appears.
I googled it and found several pages about it on “malicious webpage investigation” type sites, which all say it’s harmless.
With latest FF, it’s now like Chrome and other browsers, you can open “Developer Tools” in the browser to trace traffic without a plugin.
If it is a content delivery network source, it should still be monitored warily. Anything can be deployed this way (typically common scripts, framework code, multi-media). In theory, if content is delivered this way, it will remain cached and re-usable without re-downloading when another site requires the same objects.