Gmail, Google Search, and YouTube slow down considerably when I enable HTTP3/QUIC in Firefox, but other non-Google QUIC-utilizing services/sites do not suffer from that problem. Enabling QUIC in Chrome/Chromium-based browsers does not slow down Gmail, Google Search, and YouTube. Could it be that Google deliberately prevents Firefox from benefiting from QUIC? QUIC is more or less a Google invention. I made sure that QUIC was the culprit of slow-downs by using Wireshark to capture and analyze packets. QUIC was definitely the problem, but again, only for Google services/sites. There may be another reason for it. Firefox has stricter anti-tracking and anti-ad rules and anti-ad-oriented browsers, like Bromite (for Android) disable QUIC by default because it can bypass ad-blockers and firewalls.