Speed test results lower for Firefox - Memory leak?

[Ed1]

I have gigabit internet service from Xfinity, which has a theoretical maximum wired speed of 1.2 gbps. When I run Xfinity's speed test on Firefox multiple times, I am getting results of 450 mbps to 700 mbps. If I run the same test using Edge browser, the results are consistently about 930 mbps.

The incoming service line and speed have just been checked by an Xfinity technician, with no problems found.

I have deleted the Firefox browser cache, with no change in speed test results. I am using Firefox 94.0 beta 9, but the speed readings were the same with Firefox 93. The computer is connected to the Xfinity modem with a Cat7 cable.

What could account for the slower internet speeds using Firefox?

[Ed1]

Also, I have restarted Firefox in "troubleshooting" (safe) mode. No change. Internet speed is about 40% to 50% lower in Firefox than in Edge. I've confirmed the same results in two different desktop computers connected by ethernet cables (one is Cat7) to my network. Both have 32 GB of DDR4 RAM, one is Windows 10, the other Windows 11. Using 64-bit Firefox on both.

And, the Windows task manager shows Firefox 93 in safe mode using anywhere from 3,700 Mb of memory to over 6,000 Mb on the Windows 11 computer. Edge is showing 210 Mb.

Is there a serious memory leak in current Firefox versions?

[therube]

As a test, test in a new, clean Profile.

And, the Windows task manager shows Firefox 93 in safe mode using anywhere from 3,700 Mb of memory to over 6,000 Mb on the Windows 11 computer.

With just what open?
(Not that I want to know, but the point is you've got to have something "substantial" going on there.)
3.7 go 6.0 GB is a LOT (IMO) regardless of what might or might not be open.

On a new, clean open of FF, I'd figure ~400 MB, maybe less.

Edge is showing 210 Mb.

Without looking, I'd question that, but I suppose it is possible.

If you test a different "speed test" site, http://www.dslreports.com/speedtest, how do things there compare?

[Ed1]

Thanks for your thoughts on this, @therube. I'm going to check again using the test site you suggested when I get back home in a couple of days.

[Mike109]

Comcast recently increased my download speed from 400 to 600Mbps. Previously I usually got about 465Mbps whether I used Firefox or Edge and either the Xfinity speedtest or the Ookla speedtest.

Now when using the Ookla test I typically get about 700Mbps using either Firefox or Edge. But sometimes the Xfinity speed test gives me slow results. I started playing around & it appears Firefox is the culprit.

With either browser the Xfinity test starts at about 600 & immediately jumps to about 700. It pretty much stays there when using Edge. But with FF it keeps getting slower & slower and usually ends up in the low 500s & a few times about 480.

I've done several back-to-back tests between the two browsers yesterday & today & always get the same results. The Xfinity test gets dragged down when using Firefox.

[Ed1]

@Mike109, I can confirm what you are saying. I've just run the Ookla and Xfinity speed tests multiple times using Firefox, Chrome and Edge.

With my 1.2 Gbps service from Xfinity, I am getting these download speeds for the latest runs on each browser:

Firefox: 528 Mbps (Xfinity), 945 Mbps (Ookla)
Chrome: 924 Mbps (Xfinity), 904 Mbps (Ookla)
Edge: 906 Mbps (Xfinity), 918 Mbps (Ookla)

With the Firefox (Xfinity) test, I also see the speed start out at a high rate (usually around 900 Mbps) which drops throughout the test until a much slower final result is reported.

So there is obviously an issue with Firefox and the Xfinity speed test. If I get inspired, I may give Xfinity tech support a call to let them know about this.

Also, with 2 tabs open on each browser for the 2 speed test sites, RAM usage seems to be sitting at:

Firefox: 498 Mb
Chrome: 774 Mb
Edge: 764 Mb

Thanks for your information, which confirms what I am seeing.

[Mike109]

@Ed1
Thanks for the reply.

I also tried a fresh FF profile with Xfinity and got the same results. However the new profile displayed a different Xfinity page which had a circular speedometer display much like the Ookla test. However the Xifinity test that I'm used to seeing has a small spaceship speeding through space. Which Xfinity image do you get?

I contacted Xfinity a few days ago & they were able to pull up & show my tests results from the last week or two. It shows speeds from the high 400s up to 700, but I don't know which browser gave which speeds. They mentioned different things can affect the speed such as how busy their server is. But they said my speeds were within spec. I asked what the minimum spec was for the 600Mbps plan and am waiting to here back from them. However I didn't realize it might be a browser issue when I last contacted them so this is new information I'll mention when they get back to me.

I'll post back after hearing from them. If you're going to contact Xfinity please let me know what they tell you.

[Ed1]

@Mike109, for Xfinity tests, I am getting the page with the rocket ship blasting off with all of the browsers. In my case, I wouldn't think that fairly consistent readings at half the rated/purchased speed would be in spec. But in reality, there is probably no issue with the line or my computer as only the Firefox/Xfinity test produces this slower test reading. This would point to a Firefox issue, or maybe a Firefox/Xfinity issue.

I'm not sure I will have the time to contact Xfinity/Comcast soon, but if I do I will post any info they provide on this issue.

Thanks.

[Mike109]

I didn't notice this until now, but the Xfinity speedtest that came up with the speedometer display was "os-speedtest.xfinity.com". Not sure why that came up when using the new FF profile or what it does that is different. But I got poor results using it with Firefox.

[mgagnonlv]

My tests with speedtest.xfinity.com show a 25% lower performance in the download speed with Firefox vs Chrome or Vivaldi. Upload speed is similar.
On the other hand, I get exactly the same results with the OOkla test (https://speedtest.net)

With XFinity :
Firefox :  365.7 Mbps • 41.9 Mbps
Chrome : 452.6 Mbps • 39,2 Mbps

With Ookla (speedtest.net)
Firefox :   452,75 Mbps • 56.92 Mbps
Chrome :  451.95 Mbps • 56.78 Mbps

By the way, my rated speed is 400 Mbps • 50 Mbps and I have a wired connection.