Speedtest half speed upload using IPv6 and Firefox

Could anyone make suggestions as to why this might be?





This is on a desktop using wired Ethernet.

I'm seeing similar results with other speed checkers, so it's not just a quirk of the tbb speed test.

However using different browsers (Chrome, IE and Edge tried) to run the tbb test all gave IPv6 uploads around 17-18Mbps as did a test run using the Android version of Firefox on my phone.

http://labs.thinkbroadband.com/speedtest/ sees a similar IPv6 50% upload speed reduction.

Edited by jelv (Wed 17-Mar-21 21:08:52)

Can you replicate on your net with another Windows box running Firefox?

Yes - exactly the same. IPv4 Firefox OK, IPv6 Firefox slow, IPv6 Chrome OK.

As it's half my first though was packet fragmentation and MTU. But why would that only affect tests run using Firefox?

I've just looked back at speed test results in my profile and I have in the past had correct upload speeds using the same PC, Firefox and IPv6. However what has changed since:

1. ISP
2. Router
3. Windows updated to 20H2
4. Several Firefox updates

Given it’s solely affecting Firefox under windows in more than one machine, but not other machines (or other browsers on original machine) then I would be more inclined to look at the interaction of these updates:

3. Windows updated to 20H2
4. Several Firefox updates

In reply to a post by jelv:

I've just looked back at speed test results in my profile and I have in the past had correct upload speeds using the same PC, Firefox and IPv6. However what has changed since:

1. ISP
2. Router
3. Windows updated to 20H2
4. Several Firefox updates

IDNet, Firefox Beta v87.0 64-bit, Windows 20H2, nominal 80/20 line and TBB speedtest recording 16+Mbps upload on both IPv4 and IPv6 whether logged in or as guest.

That is interesting. I have been suffering various problems with my Internet connection and BT have changed my profile (reduced speeds have improved stability). However, that is a separate matter.

Recent tests indicated that upload speeds had declined disproportionally, so I have just performed a new series of tests, using Firefox 86.0.1 (64-bit) and Microsoft Edge Version 89.0.774.54 (Official build) (64-bit). The operating system is Windows 10 Home 20H2 (10.0.19042 Build 19042).

Today's tests revealed the same phenomenon. Upload speeds were 6.66 Mbps with Edge and only 1.77 Mbps with Firefox,

The latest Firefox update has also changed other settings, with an adverse effect upon the result, when it prints graphics from a web page...

What router are you using? Mine is a Fritz box 7530.

I've seen some reports of printing issues following the latest Windows updates. A friend is finding that printing a full page pdf image the middle of the page is blank.

In reply to a post by jelv:

What router are you using? Mine is a Fritz box 7530.

I've seen some reports of printing issues following the latest Windows updates. A friend is finding that printing a full page pdf image the middle of the page is blank.

The router is a BT Smart Hub (Homehub 6).

I noticed the difference with printing, when I printed the additional diagnostics page from the BT Wholesale site at https://speedtest.btwholesale.com.

The results page shows two green and red bars, which compare actual results against the IP Profile for the line. Those bars appear on the screen and they were previously included in the print. But now, they are missing from the print, unless I select the "Print backgrounds" option. The page has heavy backgrounds, so that uses a lot more toner or ink.

I'm not seeing v6 slowdown systematically on a 1Gbps connection (not getting full speed as on wifi).. it varies a bit but not consistent v4 vs v6 upload issues on MacOS + FF