You said the download speeds are the same whether or not your streaming Try this it is an add on to FF and it has made a dramatic increase in my speeds.
It is called Better Privacy 1.66 you can find it in the Mozilla add on's. What I believe is happening is something called .sol cookies they are hidden and CC wont find them.
A lot of This you probably know but some of it is new and very enlightening.
I think MU adds LSOs that regular cookie/cache cleaners don't pick up. I used to have these problems sometimes even after I cleaned everything out, restarted, etc., and would do a computer search for MU and find ".sol" items from MU ( I have no idea what these are). I would delete them & that would help.
** The best solution was that I added this FF Better Privacy add-on, set it for "delete all LSOs every time I close the browser", and have had very few glitches since. https://addons.mozilla.org/en-US/firefo ... erprivacy/
** Also, in your FF Tools>Options>Privacy settings, make sure you have unchecked the box about storing 3rd party cookies-- some ads will help unrelated sites (like MU) track you this way. Also, if you have facebook or other social networking sites, they will track where you go without your real permission--you have to go into the site and "opt out" of this feature. There are multiple ways sites like MU, Amazon, Google can track your use & leave behind info bits that might mess up your use of MU. I tend to be a stickler for eliminating all stored cookies regularly.
**If your computer says you are still connected to MU through FF, even though you tried to disconnect, then go to your computer Task Manager>Applications and end all tasks. Sometimes it helps to go to TM>Process and just shut down the FF app completely (It will always restart again when you connect). Usually then, I do CC, & shut down and reboot the computer. Then, reboot the router. Things are usually back to normal.