level1techs.com domain can't be opened in Firefox browser

[AuRiMaS666]

Please answer the following questions for yourself before submitting an issue

• [x] Filters were updated before reproducing an issue
• [x] I checked the knowledge base and found no answer
• [x] I checked to make sure that this issue has not already been filed

AdGuard version

7.22.0, 7.21.3 and earlier

Browser version

Firefox 143.0.4 (64-bit)

OS version

Windows 11, 24H2 (OS Build 26100.6584)

Traffic filtering

• [x] yes, I do

Ad Blocking

AdGuard Base filter

Privacy

AdGuard Tracking Protection filter

Social

AdGuard Social Media filter

Annoyances

AdGuard Cookie Notices filter, AdGuard Popups filter, AdGuard Mobile App Banners filter, AdGuard Other Annoyances filter, AdGuard Widgets filter

Security

No response

Other

No response

Language-specific

AdGuard Russian filter, EasyList Lithuania

Which DNS server do you use?

Cloudflare DNS

DNS protocol

DNS-over-HTTPS

Custom DNS

HaGeZi's Pro DNS Blocklist

What Stealth Mode options do you have enabled?

No response

Support ticket ID

No response

Issue Details

In Firefox, the domain https://level1techs.com/, and it's subdomains like https://forum.level1techs.com/ and https://winraid.level1techs.com/ are stuck in perpetual loading state while opened for the first time with Protection enabled. If these pages were opened with Protection disabled and were cached by the browser - they tend to open normally after that. Hit Ctrl+F5 to override browsers cache to reproduce the initial loading state.

https://level1techs.com/ seems to load at first, unlike both forums subdomains, but still is stuck trying to reach some third party domains.

Expected Behavior

No response

Actual Behavior

Adguard Browser Assistant is also stuck on "Adguard is launching...". When domain is whitelisted, nothing changes. Protection has to be fully disabled within the Desktop app for the page to finally open.

In comparison, MS Edge has no issues opening these domains with Protection enabled.

Screenshots

Protection enabled

Protection enabled and domain whitelisted

Protection disabled

Additional Information

This is not a recent occurrence and was observed with Adguard versions 7.22.0, 7.21.3 and earlier.

[AuRiMaS666]

Even with all filters toggled to off and main protection toggle left enabled, issue still persists.

[anyakushin]

@AuRiMaS666 This issue is related to the Firefox bug and how it handles dropped QUIC connections. It was investigated as part of the https://github.com/AdguardTeam/AdguardForWindows/issues/5661

To prove this, you can perform the following steps:

• open about:config page in Firefox
• find network.http.http3.enable and set it to false
• restart the browser

After that the site and it's subdomains should be loaded correctly with enabled protection in AdGuard.

[AuRiMaS666]

Funnily enough, I have discovered myself that this could be related to QUIC a couple days ago, but forgot to post a follow up here.

Only I have actually enabled HTTP/3 filtering in AG advanced settings and set Firefox's network.http.http3.disable_when_third_party_roots_found to false, like instructed in the knowledge base.