riots.im hosts every Element version in a sub-folder, meaning that browsers share your cookies and your session between them. This page uses sub-domains for the versions and proxies this to the corresponding version on riots.im so your browser keeps cookies etc. separated between versions.
.) in the version with an xr.ems-support.element.dev
For example, version v1.11.80 of Element, available on
https://riots.im/1.11.80/, is accessed through
https://v1x11x80.r.ems-support.element.dev/.
Also works with rc's. https://riots.im/1.11.80-rc.0/ is at
https://v1x11x80-rcx0.r.ems-support.element.dev/.
If you get an access denied error, that likely means the version you entered doesn't exist on riots.im.