Quote:Firefox users who try to open the web version of Skype in the Firefox browser run into a wall currently because Microsoft claims it is not supported.

If you try to open the page in Firefox or any other non-Chromium-based non-Microsoft Edge browser, you are greeted with a "browser not supported " message.
Update: this has been going on for about 2 years apparently.

According to the message, Skype for Web supports only Microsoft Edge and Google Chrome. Microsoft asks users to either use one of these browsers -- or other Chromium-based browser without stating so explicitly -- or use the desktop program instead. A link to the desktop version of Skype is provided.

Skype for Web is available as a preview currently, and it is possible that Microsoft will unlock it for other browsers, e.g. Firefox by Mozilla, when the web service exits the preview phase. It is equally possible that Microsoft won't do so.

Microsoft does not reveal why Firefox is not supported. It is likely that Microsoft checks the user agent of the connecting browser and uses it to determine whether users get the "browser not supported" message or access to the Skype for Web preview.

Full reading: https://www.ghacks.net/2019/01/30/skypes-for-web-does-not-support-firefox/