New Plusnet Fibre Speed ?

[#1]

Firefox 19.0.2 on Windows 7 64bit
Any reason why running the speed test through firefox is so much slower than when through chrome or IE?

[#2]

Actually, just updated Firefox to version 20.0, no change in regards the Down speed.
I decided to physically time the BTW download test in both firefox and chrome.  Guess what, both took around 13 seconds to complete the download test.... Firefox gives me a down speed of 43.78Mbps and chrome gives me 73.58Mbps
Does this suggest that using Firefox wont actually slow you down?

[#3]

It's possible that the test runs for a fixed time rather than a fixed amount of data.
I suggest downloading a fixed size test file from Thinkbroadband http://www.thinkbroadband.com/download.html and time that in each of the browsers. The 200MB file should provide a suitable test though 512MB would be practical for a longer duration.
Note: for these files 1MB = 1024KB = 1024 x 1024 (1048576) bytes.

[#4]

Well, it will be interesting to see the results from a fixed size file, but somehow I'm not going to be too surprised if it's not much different.
Also try the BTw test again with all your add-ons disabled, if there's any difference, try enabling add-ons one at a time until you find the culprit.
I would be incline to go to Mozilla's forums and leave some comment there as well as the add-on page if there's one causing the issue.

[#5]

It looks as though my suspicions were correct.....actually I've got some pretty interesting results
First I ran the think broadband speed test in firefox, then in chrome.  Suprisingly, I managed 73Mbps download in firefox and 72Mbps in chrome.  Here I was thinking that somehow the issue has resolved itself.... but to confirm, I ran the test in firefox again and got about 51Mbps, so I guess it hasn't been resolved.
However I also ran the think broadband download test twice in each browser.  I downloaded the 1GB test files (1024MB) and the results are below:
Firefox - 1st test - 2 mins 36 secs  ----  2nd test - 1 min 47 secs
Chrome- 1st test - 2 mins 47 secs -----  2nd test 2 mins 45 secs
1 minute got shaved off the download time in firefox second time round....... to be sure, I ran it again in Firefox for the third time.  The download completed in 1 min 57 seconds.
Average speed through chrome was about 6.2MB/s and through firefox third pass was around 8.8MB/s.  Second time was around 9.6MB/s average.
This suggests that Firefox is actually a lot quicker!  So not sure why it still scores low on speed tests, when it clearly is very fast with proper downloads.  The average speed of 9.6MB/s (rounded up, actually 9.57) translates to 76Mbps.  Whereas chrome 6.2MB/s translates to 49Mbps
This is the complete opposite of what the speed tests show!!!!!

[#6]

Most of the standard speedtests these days rely on Flash. TBB did have one that was not Flash based but have replaced it with the "Download Test" files.
To me, the problems you've seen suggest that Firefox is not behaving nicely with Flash for some reason - whether this is because of a recent Flash update or a Firefox one, I don't know, but I'd certainly go and comment to Mozilla.
Who knows what the potential effects on video streaming may be 

[#7]

Have you tried http://speedof.me/?
This one is html5, rather than flash.

[#8]

Hmm, I'll need to investigate further later, (other commitments right now) but first impressions are not good.