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Can't sign in to Firefox – “Unexpected error” for *any* email #20430

@exsquid

Description

@exsquid

New member and my first post on GitHub. After trying to resolve this myself, I came here after reading about a similar problem on reddit: https://www.reddit.com/r/firefox/comments/1hqx3bo/tried_to_reset_mozillafirefox_account_password/

I selected Blank Issue because I'm not sure if this is a bug or the result of changes in corporate policy. Regardless, I will use the Bug template for structure.

Description

Received a new work laptop (NEW) to replace aged/damaged work laptop (OLD) that was initially assigned to me about 2 years ago as new hire. Both are corporate-managed, but due to my role, I have a relatively high degree of freedom on the devices. Not sure how to describe it though, it's like local Admin rights with some corporate guardrails.

A few days ago I installed Firefox on NEW laptop and attempted to Sign-in to sync Firefox without success. Tried a few suggestions like disabling Zscaler, reinstalling (run as Administrator & from Microsoft Store), restarting, and clearing cache to no avail.

At the same time, the OLD laptop I'm still using was still signed-in and syncing perfectly. However, I somehow broke that too on my OLD laptop during my troubleshooting and testing when I messed with the profile feature, namely the copying and management part.

So now I'm apparently having the same problem on both laptops. I can still sign-in on my personal Android phone, which also has a separate Microsoft In-Tune Work profile.

On both work laptops I'm able to use Microsoft Edge to successfully sign-in.

Steps to reproduce

Using both Firefox and Edge on both OLD and NEW laptops, I'm simply trying to sign-in at: https://accounts.firefox.com/

First 2 screenshots are on NEW laptop, the remaining from OLD laptop.

Image Image Image Image Image Image

Expected result

Email accepted and sign-in progresses successfully as demonstrated in the Edge browser screenshots.

Actual result

Edge works while Firefox returns “Unexpected error” using any email I submit.

Environment

OLD laptop had Win10 when I first received it and installed Firefox. Last year it was updated to Win11 and Firefox has also been updating and syncing up to this point.

Currently:
-OLD Laptop-
Firefox 150.0 (64-bit)
Edition Windows 11 Enterprise
Version 23H2
Installed on ‎5/‎16/‎2025
OS build 22631.6783
Experience Windows Feature Experience Pack 1000.22700.1108.0

-NEW Laptop-
Firefox 150.0 (64-bit)
Edition Windows 11 Enterprise
Version 23H2
Installed on ‎1/‎15/‎2026
OS build 22631.6936
Experience Windows Feature Experience Pack 1000.22700.1108.0

┆Issue is synchronized with this Jira Task

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