A strange thing happened yesterday (I use Firefox 41.0.2). My down speed dropped from the 'normal' 35'ish to around 1, occasionally 2. Up took a drop but a smaller percentage.
I started the 'ticket' with my ISP and ran the requested BT speed check which gave just over 2 down.
On a whim, I decided to run the TBB speed test in IE - all 'normal'! At this point I did a Firefox 'Refresh' which returned my speeds to 26'ish down. Not sure why tihis can happen?
I will be checking Firefox in 'safe' mode soon.
I have cancelled the ISP ticket!