2010826 - ChatGPT fails to load when Brotli (br) is enabled; works when br is removed from network.http.accept-encoding.secure

Status: RESOLVED DUPLICATE of bug 2010712

(Firefox :: Untriaged, defect)

Description

[Richard Hewett]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:147.0) Gecko/20100101 Firefox/147.0

Steps to reproduce:

Use Firefox with default networking settings
Ensure network.http.accept-encoding.secure includes br
Visit https://chat.openai.com
Attempt to send or receive messages

Actual results:

ChatGPT fails to function correctly
Responses may not render, stall, or fail mid-stream
Network activity appears to continue, but content is not displayed

Expected results:

ChatGPT loads and streams responses normally, as it does in Chromium-based browsers
Firefox should correctly decode Brotli-compressed streamed responses

Comment 1

[Richard Hewett]

Additional Testing

• Disabling HTTP/3 (network.http.http3.enabled = false) does not resolve the issue
• Re-enabling Brotli after disabling HTTP/3 reproduces the failure
• Issue appears independent of HTTP/3 / QUIC

This seemed to begin around 5am EST

Comment 2

[[e-mail]]

Setting network.http.dictionaries.enable to false works around the issue, but I'm unsure of the implications of that for other sites.

Comment 3

[Richard Hewett]

The workaround used seems to have detrimental effect on Amazon.com.

Comment 5

[Andrew McCreight [:mccr8]]

A fix for this is being released in Firefox 147.0.1.

Comment 6

[Andrew McCreight [:mccr8]]

(In reply to Richard Hewett from comment #3)

The workaround used seems to have detrimental effect on Amazon.com.

What is the problem exactly?

Comment 7

[Richard Hewett]

Attachment: Screenshot 2026-01-16 130829.png

This is how Amazon.com headers look with br disabled.

Comment 8

[Richard Hewett]

Footers look equally broken.

Comment 9

[Andrew McCreight [:mccr8]]

Did you set network.http.dictionaries.enable to false, or did you do the other workaround where people were removing br from the list? The former is what we're shipping to people, and Amazon works fine for me on Nightly like that, for what it is worth.

Comment 10

[Andrew McCreight [:mccr8]]

Oh, sorry, I missed that you said that you removed br from the network.http.accept-encoding.secure pref. You should use the other simpler one instead, or just let your browser update. But you should still remove the br workaround in case it causes other problems.