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Hello,

I have a problem with YouTube videos not playing on any website when using Mozilla Firefox. Whenever a site (like zamunda.net or other forums) embeds a YouTube video, I get the following message:

“Error 153 – video player configuration error” or sometimes “For your protection, this page will not allow Firefox to display the embedded content. To view this page, you must open it in a new window.”

If I open the same video directly on YouTube (youtube.com), it plays fine. This issue happens on all websites that have embedded YouTube videos, not just one.

Windows 11 25H2

Firefox Last Version

Could this be related to codec support (H.264 / MSE) or a security restriction with embedded frames? Any suggestions on how to fix or debug this would be appreciated.

Thank you, Panche

Substack tells me that Firefox relay is blocking my posting on their site. You show me a 404 error. WTH is up? Do not block my posts please. If you have a problem, tell me and I'll remove you as my browser. Easy. Thanks

How do I clear this blocked site? This only happens on Firefox - not on other browsers, and, of course, there is no website person now at the Pirates I can connect to. It's obviously a safe site.

I keep trying to enter a shopping website I have used before in the past and keep getting the following: We block the use of VPNs and proxies to combat fraud We want you to have the best experience shopping with us! To continue, please disable your VPN or proxy.

Thank you for your patience! Your business is very important to us!

Good Morning, I have been trying to access Whatsapp web through the Mozilla browser but i have been unable now for the last four weeks. When i use other browsers then i am able to access the internet. Thank you.

Regards, Gitonga

I am trying to use a link provided by my apartment property manager. It is https://hermitagehills.loftliving.com/login When I use the link, or even type the website, on my desktop computer, using Windows 11, I cannot access the website. However, if I use any other device the website address works fine. I looked to see if I have the website blocked, but cannot find where to do that in Firefox. I know I have not blocked this website address. Can you help give me some suggestions? Thank you.

Why am I getting error messages on conservative sites. I am being denied my right to get all information right and left. Your using stupid excuses on the error messages to bar me from seeing the information. I have been on mozilla for many years and this is the first time I have had a real problem with it. The Trump report site will not let me read any content on without an error message popping up. Never had the problem a few months ago. No security problem then. Should not be a problem now unless your keeping from seeing conservative content. Let me see the content I want to see. Not what you say is a security problem.

Mozilla Corporation is sending me a box message from Nsv353A.tmp published by Mozilla Corporation teeling me to sign in to Amazon What is this?

And how do I fix this?

Hello Mozilla community

I’m troubleshooting a Kerberos/SPNEGO proxy auth issue and need help understanding whether this is a Firefox bug or a misconfiguration on our side.

Environment :

Client OS: Ubuntu 24.04 (GNOME session)

Firefox: 144.0

Other clients on same host: curl (works) and Chrome/Chromium (works)

Proxy (on-prem): swg.test.local:8080 (HTTP proxy performing Negotiate/Kerberos authentication)

AD / Kerberos realm: TEST.LOCAL (users), service SPN: HTTP/swg.test.local registered in AD

Domain trust: one-way trust exists between test.local and test.intra (contextual; but current test is within test.local)

Symptom :

curl --proxy http://swg.test.local:8080 --proxy-negotiate -u : http://example.com -> negotiates and sends Proxy-Authorization: Negotiate ... and request succeeds.

Chrome also performs Negotiate and the request succeeds.

Firefox never sends Proxy-Authorization: Negotiate and the proxy returns 407 Proxy Authentication Required. No prompt for credentials; negotiation does not start.

What I already validated

Kerberos TGT is present in user cache:

kinit user@test.local klist

TGT is visible and valid.

curl and Chrome negotiate successfully from the same host (so SPN, AD, keytab, realm mapping are working in general).

Firefox launched from terminal (so it inherits KRB5CCNAME) still does not negotiate.

I enabled KRB5_TRACE and launched Firefox; trace file stays empty (suggesting Firefox did not call into GSSAPI for this request).

Network capture shows proxy challenge Proxy-Authenticate: Negotiate and no corresponding Proxy-Authorization header from Firefox.

Firefox prefs checked / set (About:config values I validated/changed)

network.negotiate-auth.trusted-uris = swg.test.local,.test.local → Ensures Firefox will send Kerberos tokens to that host/domain.

network.negotiate-auth.delegation-uris = .test.local (optional)

network.auth.use-sspi = false (Linux)

network.negotiate-auth.allow-non-fqdn = false

network.automatic-ntlm-auth.trusted-uris left blank or set to .test.local

Despite network.negotiate-auth.trusted-uris containing the exact FQDN and domain, Firefox still does not attempt negotiation.

Diagnostics already captured

tcpdump pcap covering UDP/TCP 88 and proxy port 8080 (shows proxy 407 and absence of Proxy-Authorization from Firefox)

KRB5_TRACE=/tmp/krb5_trace.log for Firefox launch (no GSS calls logged)

Reproduced curl/Chrome flows that do include Proxy-Authorization: Negotiate ...

Hypothesis

Firefox is refusing to attempt Negotiate at all — likely due to either:

a preference that’s still missing or misinterpreted (trusted-uris format, wildcard/domain handling), or

a desktop-launch / environment isolation problem (GUI-launched Firefox not seeing Kerberos credentials or environment), or

a bug/regression in Firefox’s GSSAPI/SPNEGO integration on Linux (e.g., refusing to use a credentials cache inherited from the shell, or ignoring network.negotiate-auth.trusted-uris for proxy authorization specifically).

What I need from the community

Has anyone seen Firefox on Linux behave this way (curl/Chrome work, Firefox never starts Negotiate) with an on-prem proxy using Proxy-Authenticate: Negotiate?

Any additional about:config prefs or hidden flags that affect proxy SPNEGO (not site SPNEGO) that I should check? I already set network.negotiate-auth.trusted-uris.

Any differences in behavior between Firefox launched from GUI vs. launched from terminal that might cause the client not to use the Kerberos ticket cache — and reliable steps to reproduce/diagnose?

If you have a small reproducible test case or a recommended debug build/flags to capture verbose Firefox GSSAPI logs (beyond KRB5_TRACE) please share them.

If this is a known bug/regression, pointer to the bugtracker entry would be appreciated.

Thanks in advance

Bonjour, Depuis deux jours, je ne peux plus me connecter à ma banque, alors que tout fonctionnait très bien auparavant. Pouvez-vous m'en expliquer la raison et me dire ce que je dois faire. Cordialement