Inconsistent speedtest.net results (slow in Firefox and Chrome)

I've been thinking my HP laptop was a bit sluggish lately. After the latest Windows 10 updates, I ensured all drivers are up to data, had clear out, deleted cookies and cache etc. Ran superantispyware, malwarebytes and ccleaner. All clear. I then ran speedtest.net in Firefox and also Chrome which I both use. I was getting about 30 Mbps download speeds. My package is for 100 Mbps. I then ran the test in Edge (which I don't normally use) and this gives 110 Mbps. I then ran the Windows 10 Speedtest app, this also gives 110 Mbps. I have run firefox in safe mode, switched hardware acceleration options etc, nothing changes. Have even done a full settings reset in Firefox. Everything is set for System no proxy details. Wired ethernet. Nothing else running at the time. Is there a reason/solution why Chrome and Firefox seem slow on the laptop? I have a similar setup on my desktop and this gives me 110 Mbps across all 3 browsers. Any ideas? Thanks.


EDIT to add; If I start Firefox by "Run as administrator" I get about 70 Mbps. So Better than 30 but still not 100+. It's WIndows 10 Home and I am an administrator so don't know why this makes any difference but maybe it adds some clues?

When you run it is it using the same server as often it will find one a long way away

Samuria said:

When you run it is it using the same server as often it will find one a long way away

Yes thanks, I noticed it was selecting different ones but changing the server made no difference.

Starting to wonder if the cpu isn't fast enough to measure the faster downloads speeds with the overheads of the browser. It is only a 2.2 Ghz. (2.5 Boost) dual-core. Does that seem reasonable or is something not right? The more drivers I disable (sound/graphics) etc. the faster it goes but there is no one thing that bumps it right up. Task manager shows cpu going up to 90% when busy/testing but there is nothing else running that shouldn't be.I only have WIndows Defender, no other AV. What I still don't understand is why the download is twice as fast, when I run Firefox in administrator mode, why would that affect it??

Finally found the solution in Firefox Quantum.

Set browser.tabs.remote.autostart = false in about:config. Default is true.

Apparently switches to single processor mode, which is better in less high spec systems.

Difference is absolutely astonishing. Now getting 115 Mbps in speedtest.net instead of about 30. It is using much less cpu and much less memory. Websites load straight away again instead of seeming to pause multiple times and taking 10+ seconds to complete, switching tabs is instant instead of getting delays, reloads and spinning circles. Flash isn't dead slow again (I use it on a couple of sites) and HD videos don't stutter again.

I'm sure this must have started one or two Firefox Quantum updates ago but it coincided with various other updates at the same time.

I was seriously considering complete Windows 10 reinstall too!!!!

(In case anyone is dubious, I have switched the setting back and forth several times over 24 hours and it is totally repeatable)

Put about:config into the url line at the top of the screen. Accept the "risk". Put browser.tabs.remote.autostart into the search. If will tell you if a value is the default or "modified". Double click to toggle the value. Keep a record of anything you change, though, just in case. Restart firefox for changes to take affect.

UPDATE: Although my computer was working acceptably with the above browser.tabs.remote.autostart = false setting, I installed a Windows 10 update on Thursday KB4343909. I noticed immediately, that the computer generally was very noticeably much quicker. I can now type into the taskbar search field and the results are immediate, It was previously taking several seconds after pressing each character.

I have now tried setting Firefox browser.tabs.remote.autostart back to true, the default value. I now get the proper speed either way 115 Mbps.

So the Windows update has speed up my computer and means I no longer need to use that Firefox workaround.

Looking at the Update details includes:

Addresses an issue that causes high CPU usage that results in performance degradation on some systems with Family 15h and 16h AMD processors. This issue occurs after installing the June 2018 or July 2018 Windows updates from Microsoft and the AMD microcode updates that address Spectre Variant 2 (CVE-2017-5715 – Branch Target Injection).


My Processor is a 16h. As per my opening post, the slowdown started after a June or July update. So I think we have the explanation and solution!.