We all know the statements that Microsoft made about linux. They love Linux. They even wrote a blogpost about it. But that love falls short when you use Firefox on Linux. In my research on identity and access management, I have been exploring various login options. One of the approaches I tested is passwordless login using technologies like WebAuthn and YubiKey support. I experimented with this on various operating systems, browsers and Identity Providers, including Microsoft Entra ID.

The Problem

Normaly you are presented with a prompt to allow you to choose other sign-in options:

When loading the web page on a linux distribution, I was presented with the following options:

Where was the option to use my YubiKey to login? I was sure it once worked fine in Linux on Firefox. I tried another Linux distribution and was presented with the same problem.

The search

My first thought was that it was a problem with the YubiKey. I tried another YubiKey, but the problem persisted. I installed the Chrome browser as it is the popular browser. On Chrome I was presented with the correct options, was able to choose the YubiKey and login successfully.

I verified on the Yubico website Operating system and web browser support for FIDO2 and U2F and found that the YubiKey is supported on Firefox on Linux.

So, why was I not able to login using my YubiKey on Linux using Firefox to login on Microsoft Entra ID? I did some digging on the microsoft website and found a user already asked the question. Microsoft states that they don’t support passwordless login on Firefox in Linux.

Entra ID blocks Firefox

I still needed to find out if Firefox on Linux is capable of supporting Yubikey to login. I searched for the User Agent string that Chrome is using in their browser, and I changed the User Agent string in Firefox to match the one in Chrome.

Once I update the User Agent string in Firefox, I was able to login using my YubiKey on Microsoft Entra ID.

Microsoft loves Linux, but only if you don’t use Firefox? I hope they update their support for Firefox on Linux soon.