[userbinator]

There are plenty of extensions that will let you change the UA for any site; having yet another one with such a narrow function seems to me like those "we have a smartphone app too" whose only purpose is to open the browser to their site.

[andrewshadura]

Just add this to your prefs.js/about:config

  user_pref("general.useragent.override.web.skype.com", "Mozilla/5.0 (Linux) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.77 Safari/537.36");

[hawski]

But if it's your only use of such a thing, as it is for me, it's just one click away. You can also feel reasonably safe as the extension works only on Skype's web sites per Web Extension manifest.