BIG Drop in speed

[#1]

Hello,
Not sure why but I've seen a massive drop in speed, from ~68/15 down to ~42/9 (simlar results from BT and Speednet).
When I ran the diagnostics test from BT it reported that I was getting 56/10 against a profile of 61 / 20.
I've reset the modem and the router (Airport Extreem) but no change.
Anyone seen similar issues?  Any 'testing' going on?
Thanks, Sean.

[#2]

Hi there,
I can see you've raised a fault so we can have a deeper look into this and see if we can identify any issues. I've run a few tests and can't see anything obvious I'm afraid but our faults team should get back to you ASAP about this.

[#3]

Thanks for looking into this.

[#4]

OK something very strange going on.  Here is the result using Firefox -

Here is the result using Chrome (IE is the same)

Firefox was reporting the same speed previously so not sure what's gone wrong!
Looks like while there is a drop (~10Mbps) it is not as bad as it looked.
Anyone seen similar issues?