Use old C3 releases?

I have a project folder, but my desktop editor is using from the latest stable release, but I need to go back to older beta releases open instead.

I know you can go to old releases like this: editor.construct.net/r165

But the browser editor doesn't accept project folders, only c3p files.

How do I use an old release?

You can also just save as single file in the desktop build to get a .c3p. As it happens there is also experimental support for opening folder projects in the browser.