(1623340) Firefox compatibility with Microsoft Teams and Teams for friends and family

User agent overrides

Spun off from https://bugzilla.mozilla.org/show_bug.cgi?id=1623340#c5

A fix would be for Firefox to spoof its own user-agent string, so it represents itself as whatever the latest version of Edge is.

The functionality works, but Microsoft is blocking it through user-agent sniffing. …

Firefox could spoof the user-agent when any Microsoft site is visited (based on a list of primary domains, perhaps). …

… In addition to the HTTP User-Agent, changes may also be needed to data in the window.navigator object to circumvent this.

Earlier this week I began testing this Edge string (the latest):

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.102 Safari/537.36 Edg/85.0.564.51

– overriding these two URLs:


– specified in Custom UserAgent String added to Firefox 80.0.1 on FreeBSD-CURRENT.


Meet in a group context: a moment after apparently beginning the meeting – the camera image appears as it should – the image disappears, leaving an alert:

Sorry, we couldn’t connect you.

– and two buttons:

  • Retry
  • Dismiss

– retries do not succeed.

Unwanted effects of the override include breakage of OneNote:

Sorry, we ran into a problem.

Your feedback helps Microsoft improve OneNote. Give feedback to Microsoft

  • Restart

– restarts lead to the same problem.

Without the override for the two domains

OneNote works:

With the override for https://teams.microsoft.com/ alone

OneNote breaks.

With the override for https://statics.teams.cdn.office.net/ alone

OneNote works.

Meet in a group context results in an explicit alert, before the AV dialogue:

Use the app or a supported browser


any news on this issue?
Thank you

On the Mozilla side: none that I can see.

On the Microsoft side:

Off-topic: Zoom

From @andreip at https://microsoftteams.uservoice.com/forums/555103-public/suggestions/36946039-calls-support-in-firefox-mozilla:

This is why I use Zoom. Zoom just works on the web in Firefox.

I should not encourage use of Zoom.

Recently I was invited to two meetings – online rallies – both of which included an invitation to join from the browser, both of which failed when the invitation was accepted. Poor user experience.

The first meeting – using Microsoft Edge on Windows 10 1909 – was particularly troublesome, because the failure directed me to download Zoom from Microsoft’s Store, in a managed environment where it was impossible to do so. I was forced to go elsewhere and use a different computer.

A screenshot of the second failed meeting – Google Chrome on FreeBSD-CURRENT:

– less troublesome than the first, in that download of the installer for Zoom succeeded (without requiring Microsoft’s Store) but still, a poor user experience.

I was misled (by Zoom) into believing that Zoom would work in web browsers, but it didn’t, and the discoveries caused me to miss the beginnings of both meetings.

From https://github.com/webcompat/web-bugs/issues/25070#issuecomment-743936967

… I was able to record even a call in zoom. It works well for me.

I don’t doubt it :slight_smile: but I should not recommend use of a service that misrepresents itself.

Nightclub organiser:

Come to our club tonight! No footwear restrictions. Just register in advance.


Your name’s on the list. Come in! No footwear restrictions. Now turn around. Go away. You can’t come in wearing trainers. Go to that shoe shop – over there – register and sign in over there to get a pair of shoes that suit our non-advertised restrictions.

Shoe shop:

Welcome! Thank you for signing in; we require this before selling shoes. Now turn around. Go away. We’re not allowed to sell shoes to you.

teams.live.com (Teams for friends and family)

I lazily use this override:

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.102 Safari/537.36 Edg/85.0.564.51

It’s enough for text chat but (as expected) not enough for video.


Re: https://github.com/phts/firefox-web-skype/issues/9 I now (more lazily) use web.skype.com for Firefox

Any news on this? This is what I get when I spoof with Microsoft Edge:


What are the technologies used by Microsoft Teams that Firefox doesn’t support? Why we can’t just implement the support on our own after spoofing?

From https://github.com/webcompat/web-bugs/issues/25070#issuecomment-751324990:

… MS Teams so far only supported Chrome’s proprietary Plan B for SDP used in WebRTC. Teams switched to the standard way (aka Unified Plan) of doing things, but are facing now issues from designing everything around Chrome initially. …

Microsoft 365 Roadmap

@drno @karlcow hi, no mention of Firefox, Plan B or SDP on the roadmap.

Please, can you think of any other phrase that Microsoft might use when, eventually, mapping occurs?

Microsoft Teams UserVoice

Calls support in Firefox (Mozilla) – Microsoft Teams UserVoice

  • 415 votes


From https://microsoftteams.uservoice.com/:

Microsoft will be moving away from UserVoice sites on a product-by-product basis throughout the 2021 calendar year. We will leverage 1st party solutions for customer feedback. Learn more

From Microsoft’s UserVoice Pages:

… a variety of channels that allow customers to communicate with us. Including:

Microsoft Teams in Microsoft Community


  • this non-localised link will redirect to your locale.

Microsoft Teams in Microsoft Tech Community

Using the UA Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/79.0.3945.74 Safari/537.36 Edg/79.0.309.43 to override https://teams.microsoft.com/ I was able to join video calls, speak, use the chat, and OneNote

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It is awesome! I tried it with Custom User Agent addon and confirm that even desktop sharing works!

There’s a problem, as pictured in the opening post, and Restart does not resolve the problem.

Interesting, I haven’t encountered it yet

I think now there is a fix for it in firefox by an extension it uses the user agent from the Edge browser and it works flawlessly even tho there is no first-party support but at least you can now use it here is the link

1 Like

From the opening post:

This problem occurs when Custom UserAgent String is used to prefer an override for the https://teams.microsoft.com/ domain.

Details of the problem have been reported to the developer of Custom UserAgent String via the given support site, https://mybrowseraddon.com/custom-useragent-string.html.

When Teams Phone Fix is used to prefer the same override for the same domain: no such problem.

Maybe not.

At the time of writing, for teams.live.com:

  • no audio output.


– and so on.

Tested with a different profile, Teams Phone Fix can’t fix Teams for friends and family:

  • teams.live.com is out of scope for the extension.

Mozilla fixed the issue with teams and ETP on firefox 96. However, video call still requires the hack.

Hello everybody,
as already reported in the bugzilla report of Mozilla, the problem with calls in Teams still persists - both for audio and video calls - at least on my side: I use the current Nightly version of FF in Windows 10 64-bit: 106.0a1 (2022-09-05) (64-bit).
Can anyone else confirm this behavior? Is there any progress on this topic?
Thank you very much!

https://github.com/webcompat/web-bugs/issues/25070#issuecomment-1346973196 yesterday:

Good news! I was just able to use teams in a conference call without any workaround add-ons installed! Video works fine both ways.

Firefox 108.0: Mozilla/5.0 (X11; Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0.

From the subsequent comment:

… conference calls are now working on Linux with Mozilla/5.0 (X11; Linux x86_64; rv:108.0) Gecko/20100101 Firefox/108.0. …

Yesterday I joined a scheduled conference call (I clicked the Join button in a Teams area). I made no attempt to speak, other people were audible.

I made no attempt to use the chosen webcam.

After some time staring at the array of participants, whilst listening, I joined (without transferring) using an iPad.

Video was:

  • present in Teams on the iPad
  • not present in Firefox.

User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:108.0) Gecko/20100101 Firefox/108.0

From https://github.com/webcompat/web-bugs/issues/118070#issue-1579196443:

… If you spoof the browser agent to be Chrome, one on one calls mostly work.

Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/ Safari/537.36

A click on the Video call button has the following result:


  • No available camera found

– and when not aiming to make a video call, there’s the previously described breakage of OneNote:

% pkg iinfo firefox
% uname -aKU
FreeBSD mowa219-gjp4-8570p-freebsd 14.0-CURRENT FreeBSD 14.0-CURRENT #7 main-n263630-ab3e6234ab6e-dirty: Sun Jun 18 14:56:48 BST 2023     grahamperrin@mowa219-gjp4-8570p-freebsd:/usr/obj/usr/src/amd64.amd64/sys/GENERIC amd64 1400090 1400090