Pre-installed webextensions must be in profile

[thomasmo]

Per https://blog.mozilla.org/addons/2019/10/31/firefox-to-discontinue-sideloaded-extensions/ we need to update our setup to pre-install the Youtube and Vimeo webextensions into a profile folder rather than the install/system folder. This is in response to improving security in Firefox.

[philip-lamb]

Fixed in 206ed1f727f349294a00072850a32ca27f138cbf