@VincentS
I rolled your issue and question, all into:
Getting: ERR_QUIC_PROTOCOL_ERROR. The two websites that I’ve noticed with this issue are https://cdn.discordapp.com and https://www.programiz.com. I’ve checked and the error occurs in both Brave and Chromium, but does not occur in Firefox. I disabled “Experimental QUIC protocol” in brave://flags/ but now I just get the error ERR_CONNECTION_CLOSED instead. I am guessing: a bug in Chromium. But being able to open attachments on Discord is rather important and I don’t want to move all my info over to Firefox. Is there any workaround?
I suggest that you visit ‘https://alter.systems’ and enter all of that description-and-question.
‘Alter.systems’ will reply with explanations and suggestions . . . and then probably ask you:
If you tell me your OS (Windows/macOS/Linux) and Brave version, I can give you the exact steps or command-line switch for your environment. Want me to do that?
THEN, and there, reply with your Linux OS info and Brave Browser info.
Explanation I received from Alter.systems, re QUIC, TLS/HTTP3:
Background: What’s QUIC, and why it fails here
QUIC is a transport protocol invented by Google to replace TCP+TLS, supposedly making connections faster and more secure. But here’s the problem:
Chromium-based browsers (Chrome, Brave, Edge, etc.) tend to roll out experimental QUIC updates very aggressively, and they sometimes break compatibility with specific server configurations or CDNs — particularly Discord’s CDN (cdn.discordapp.com) because it uses Cloudflare infrastructure with nonstandard QUIC settings.
So when you see:
ERR_QUIC_PROTOCOL_ERROR → that’s Chrome failing to complete a QUIC handshake.
ERR_CONNECTION_CLOSED after disabling QUIC → that means QUIC is disabled, but something else (such as TLS/HTTP3 negotiation) still isn’t functioning correctly.
Why it works in Firefox
Firefox doesn’t use Chromium’s QUIC stack; it uses its own HTTP/3 implementation, which adheres more strictly to published RFCs. Chromium, by contrast, uses Google’s experimental branch, which often introduces premature behaviors that server-side software hasn’t caught up with.
Hence: Firefox works, Chromium doesn’t.
Even when you disable “Experimental QUIC protocol,” Chromium can still attempt HTTP/3 (which rides on QUIC).