Recently Linden Labs have made changes to the way that textures load in your viewer.
Some beta versions of Emerald don’t support the http textures properly and as I type ;Emerald 184.108.40.2066 is ok, viewer 2 and its betas and snowglobe should work ok, but in some sims http hasn’t been implemented.
UDP still has no plans to be phased out as far as i can see so if you are a legacy, viewer user, you should see a bit of improvement as more and more users take advantage on the http delivery and less use the UDP. Hope this is helpful.
In some places its been seems that the loading of external web pages in the internal browser makes objects and textures disappear and reappear when the browser is closed , Im guessing here that the HTTP bandwidth get used up by the browser and returned to the viewer we your browsing on the net stops.