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.te.element.dev
For example, version v1.11.80 of Element, available on
https://riots.im/1.11.80/, is accessed through
https://v1x11x80.r.te.element.dev/.
Also works with rc's. https://riots.im/1.11.80-rc.0/ is at
https://v1x11x80-rcx0.r.te.element.dev/.
If you get an access denied error, that likely means the version you entered doesn't exist on riots.im.