Firefox Community Forum

I’ve been troubleshooting a strange networking issue in Firefox that I haven’t been able to pin down, and it seems to be specific to Firefox’s network stack rather than my system or connection.

On several high-traffic sites that sit behind Cloudflare (Discord, Shopify storefronts, some SaaS dashboards), Firefox occasionally stalls during page load. The request shows up in the Network panel as pending for several seconds before finally completing. Sometimes the page partially renders and then hangs until the stalled requests finish.

A few things that make this confusing:

• The same sites load instantly in Chromium-based browsers on the same machine and network • The issue persists even in Firefox Troubleshoot Mode with extensions disabled • DNS over HTTPS on/off does not appear to change behavior • Packet captures show the TCP connection is established quickly, but some HTTP/2 streams appear to wait before data begins flowing • If I force HTTP/1.1 using a proxy for testing, the issue disappears

System details:

OS: Windows 11 Firefox: latest stable release Connection: fiber, low latency, no packet loss locally No system proxy configured

Things I’ve already tried:

• Clearing cache and site data • New Firefox profile • Disabling hardware acceleration • Testing with network.http.http2.enabled toggled • Comparing HAR logs with Chromium

One thing I noticed in the Firefox networking logs is that multiplexed streams sometimes wait behind earlier streams longer than expected, almost like there’s some internal prioritization or queue behavior happening. I’m wondering whether this could be related to HTTP/2 prioritization logic, connection coalescing, or how Firefox handles Cloudflare edge endpoints.

Has anyone seen similar behavior or knows whether there are any advanced networking prefs in about:config worth experimenting with (connection limits, HTTP/2 concurrency, etc.)?

Curious if this might be a known quirk with certain CDNs or just something unique to my environment.

Home Internet speed via cable 500 Mbps. When checking the Internet speed through the Firefox browser (version 133.0.3), incoming and outgoing about 250 Mbps. That is, the browser cuts the speed twice. When checking the speed through Google Chrome (version 145.0.7632.160), the Internet speed is about the declared 500 Mbps. Please help solve the problem with Internet speed through the Firefox browser.

Now a days every one use proxy vpn when it starts speed of net is dead browser can not work or very slow working that's why people are experimentally with different browsers to see which one does not slowdown even in slow net speed

My browser has been acting off lately, it takes a longer amount of time than usual to even open gmail. Sometimes, it just fails to connect to a server and keeps loading forever and just stops (including gmail).

Hi Firefox Team,

I wanted to ask, whether you know any solution to my streaming problem. I noticed that my download speed is incredibly fast, when I am running a download in the background of my PC. This can be a windows-update or updating a game via steam. But when I am not downloading anything, then Youtube cant even stream 360p without buffering every 10 seconds. I feel like the Firefox-Browser is not telling my PC that it needs the internet and thus does not get it, but when another program needs internet, It gets enough to work.

I can use edge and my speed tests perfect on speed test. If I use Firefox the upstream is half. I only have block installed but doesn't matter if I disable or not.

I'm on the local network. When I use Firefox to download a very small .docx file, the download gets stuck and doesn't move, taking a while to complete. But with Edge, it downloads almost instantly. Please help resolve this issue.

On Mac but not on Safari Firefox buffers for minutes before connecting. I’ve tried clearing the cache with no improvement. Until recently I never had this problem and as I said there’s no problem on Safari.

Hello,

I am having major issues with Firefox speeds, Mainly upload speeds. On Edge I am getting 400 up & down (no issues at all). However, on Firefox upload speed is 144 Mbps, same on private windows. The only issue is with Firefox. Windows is up to date and Firefox version is 139.0.4 (64-bit)

Attached comparison screenshots for reference.

Below are the steps i performed:

=========================

Firefox Troubleshoot Mode Test: Download: 411.71 Mbps (Full Speed) Upload: 173.03 Mbps (Still Bottlenecked) Extensions Disabled Manually (Normal Firefox): No significant improvement. Hardware Acceleration Toggle (Normal Firefox): No significant improvement.

=========================

New Temporary Firefox Profile Test: Download: ~333 Mbps Upload: ~190 Mbps Problem persists even with a clean profile.

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Temporarily Disable Windows Firewall Test: Resulted in ~349 Mbps Down / ~148 Mbps Up. Firewall re-enabled.

=========================

Could someone let me know how to get this fixed. Creating a new profile should have fixed issued assuming one of the extensions was causing the bottleneck. But even with a new profile its not making any difference.

Once I visit any web site that uses HTTPS there is approximately a 90% chance it'll take seconds or even minutes to secure the connection. This never happens on other browsers as they load such pages instantaneously.

I already cleaned my data up and removed the extensions, both suspected and innocent bystanders, to no avail.

As stated in the title, I'm using Firefox 139.0.1 x64 on Windows 11 (24H2, build 26100.4061). This started happening after an automatic Firefox update, I never changed anything in my system configuration.

Firefox is no longer compatible with my bank's system. I can't log in with the secure access code the bank sends to verify my identity when using Firefox. The bank says it is a problem with Firefox. Other browsers work flawlessly ... are you working on a solution? I only use Firefox unless forced to use something else ...

I'm using Mac OS 11.7.10. Firefox desktop no longer allows me to browse the internet. It just keeps spinning wheels. I've downloaded the newest version and it still crashes. What can I do?

Suddenly this morning Firefox stopped connecting to any websites. It never gives an error message, it just tries to connect forever. Chrome and Edge can both access the internet without problems. I'm running Windows 11 Pro, and here's what I've tried so far:

Malwarebytes disabled Firewall disabled Turned off all add-ons/extensions Firefox uninstalled and reinstalled Firefox, Windows, Malwarebytes, etc all updated Cache & cookies cleared Refresh Proxy use disabled IPv6 enabled DNS prefetching set to "true" Full malware scan by Malwarebytes Computer restarted (several times)

Any other ideas? Thanks!

I am having difficulty trying to view a website. I receive the following message whenever I try to view this website:

"Suspected Phishing This website has been reported for potential phishing.

Phishing is when a site attempts to steal sensitive information by falsely presenting as a safe source."

There are two buttons beneath this message, the one on the left which reads "Learn More," the one on the right which reads "Ignore & Proceed." Yet when I click on either of the buttons a blank white page appears.

The web address in the URL field also changes from the website I originally selected to the following:

https://www.smartredirect.de/redir/clickGate.php?u=IgKHHLBT&m=1&p=8vZ5ugFkSx&t=vHbSdnLT&st=&s=&url=http%3A%2F%2Fwww.brutaltops.com%2F&r=https%3A%2F%2Fwww.google.com%2Fsearch%3Fq%3DBrutalTops.com%26sca_esv%3D9a8e8f6bd3ba345e%26source%3Dhp%26ei%3DHMO2Z6SJBaqWwbkP7JzXUA%26iflsig%3DACkRmUkAAAAAZ7bRLHc87-cSI48xaawgAj9EjL-Nm71U%26ved%3D0ahUKEwikh43Vx9GLAxUqSzABHWzOFQoQ4dUDCBM%26oq%3DBrutalTops.com%26gs_lp%3DEgdnd3Mtd2l6Ig5CcnV0YWxUb3BzLmNvbUjNa1CbCliBWXABeACQAQCYAW-gAfcKqgEEMTYuMbgBDMgBAPgBAZgCCaAClwaoAgrCAgoQABgDGOoCGI8BwgIKEC4YAxjqAhiPAcICERAuGIAEGJECGNEDGMcBGIoFwgILEAAYgAQYkQIYigXCAg4QLhiABBixAxjRAxjHAcICBRAuGIAEwgIREC4YgAQYsQMY0QMYgwEYxwHCAgsQLhiABBjRAxjHAcICCBAAGIAEGLEDwgIXEC4YgAQYkQIYsQMY0QMYgwEYxwEYigXCAgUQABiABMICCxAAGIAEGLEDGIMBwgIIEC4YgAQYsQPCAg4QLhiABBixAxiDARiKBcICCxAAGIAEGJIDGIoFwgILEC4YgAQYsQMY1ALCAhEQABiABBiRAhixAxiDARiKBcICFBAuGIAEGJECGLEDGIMBGNQCGIoFwgIREC4YgAQYkQIYxwEYigUYrwHCAg8QABiABBixAxgKGEYY-QHCAgoQABiABBixAxgKwgINEAAYgAQYsQMYgwEYCsICBxAuGIAEGArCAgcQABiABBgKwgIFEAAY7wWYAxPxBQrZJeqRYy6tkgcDNi4zoAeUYg%26sclient%3Dgws-wiz

Why would I not be able to view this website (and others too) with Firefox but am able with Chrome? I want to be able use Firefox, as Chrome will not allow use of an extension that Firefox will.

Please tell me how this problem may be fixed.