There are some things you can do to reduce Texture Thrashing. A viewer restart is often all you need.
Also, remove all the HUD's. Some HUDs use a huge amount of texture memory.
In Firestorm turn off the images in chat. I don't remember if FS has fixed it, but those tiny images require the full profile image be downloaded. As these images appear in the User Interface part of the viewer it holds onto them forever, which is why a restart helps as it discards all those not currently needed