"Incorrect Device Time" error on Zoho login (accounts.zoho.eu) — server rejects on initial request, not a real clock issue

[Maddz10]

Preliminary Checks

• I have read and understood the important section above.
• I have searched existing issues and avoided creating duplicates.
• I am not filing an enhancement request.
• I have checked that this issue cannot be reproduced on Mozilla Firefox.
• I have checked that this issue can be reproduced once I removed all my Mods and Custom CSS.

What happened?

Logging into Zoho (accounts.zoho.eu) fails with an "Incorrect Device Time" error page, while the device clock is correct and the same login works fine in other browsers on the same machine/network. The error page is served directly by Zoho's server on the very first request (HTTP 200, plain HTML) — no client-side JavaScript is involved in producing it (verified via DevTools Network tab: only 3 requests total — the HTML page itself, a cached CSS file, and favicon.ico — no XHR/fetch calls).

Expected behavior

Login should proceed normally, as it does in other browsers (e.g. Chrome/Edge) on the same device, same network, same system clock.

Actual behavior

Zoho serves its "Incorrect Device Time" error page on the initial HTML response.

Steps to reproduce

Go to the Zoho login page (accounts.zoho.eu).
Enter credentials and submit.
The page immediately returns Zoho's "Incorrect Device Time" error page instead of proceeding with login.

Troubleshooting already done with Claude help:

All of the following were tested and did not resolve the issue:

• System clock verified correct (both OS-level and via Date() in the browser console).
• privacy.resistFingerprinting and privacy.fingerprintingProtection in about:config: already false.
• Tested in a Private Browsing window (rules out cookies/stored session data).
• Restarted in Troubleshoot Mode with all extensions/mods disabled.
• DNS over HTTPS: already off / using system default.
• No proxy configured (verified in Network Settings).
• Tested on a brand-new, completely clean Zen profile (about:profiles) — issue persists even with zero customization.

Since the error page comes back as a plain server-rendered response before any JS executes, and persists across a totally clean profile, this points to something in how Zen presents itself at the network/TLS layer (e.g. TLS ClientHello fingerprint, HTTP header set, ALPN/cipher order, etc.) that Zoho's server-side fraud/bot-detection is flagging — and mislabeling as a device-time issue. This does not reproduce in other browsers on the same machine/network, so it appears specific to Zen's network stack rather than to the user's system.

Screenshots and videos

No response

Version

1.21.15b (Firefox 154.0) (64-bit)

What platform are you seeing the problem on?

Windows - x64

What component is this issue related to?

Other

Relevant log output if applicable

[Propheticus]

It'd be interesting to see if the same happens in Firefox.

• Does a test like https://datetimetrack.com/time/browser-clock show the correct time and time-zone?
• Does your systems set time-zone actually match the configured time? (these can mismatch when set manually)
  also see https://help.zoho.com/portal/en/kb/accounts/faqs-troubleshooting/troubleshooting/sign-in/articles/date-and-time-incorrect

[Maddz10]

It'd be interesting to see if the same happens in Firefox.

• Does a test like https://datetimetrack.com/time/browser-clock show the correct time and time-zone?
• Does your systems set time-zone actually match the configured time? (these can mismatch when set manually)
  also see https://help.zoho.com/portal/en/kb/accounts/faqs-troubleshooting/troubleshooting/sign-in/articles/date-and-time-incorrect

Works fine on Firefox 154.0 (64 bit)
datetimetrack gives correct date time and timezone
Zen and system timezones and times match
Also already checked what zoho support mentions

[Propheticus]

Zen doesn't change anything in the networking stack of Firefox, so this difference is a bit strange.
To me it seems like you already did an extensive round of troubleshooting.

Because I don't have any better ideas at this moment. Could you check what happens when you DO use a DNS-over-HTTPS provider?

e.g.

[Maddz10]

Tried cloudflare and quad9, in both cases the error persists
Also tried on a different pc with my home internet connection and still doesn't work

[Propheticus]

I'm a bit baffled and can't think of difference between Firefox and Zen that would explain why the former works but the latter doesn't.

@mr-cheffy Did you touch any networking (necko / netwerk) code? No, right?

@Maddz10 Are you running any (corporate) security suite or could there be a network-level security that's got allow rules for Firefox but treats Zen differently? Or things like certificate authorities / root certs that have been loaded into Firefox by means of a policy or provisioning that are not in Zen?

[Maddz10]

No security policies are running, both on my work and personal PCs. Also i tried both with office and home network