Hi Chris, Firefox Nightly (currently future Firefox 80) and Firefox Developer Edition (currently future Firefox 79) install into separate folders and use their own profiles, so side-by-side installs are easy these days. You can control the install folder name/location if you download a "full" installer (use the selectors to choose your version and language):

https://www.mozilla.org/en-US/firefox/all/#product-desktop-nightly

Of course, if you have any concern at all about data confusion, a backup isn't a bad idea: Back up and restore information in Firefox profiles.

Any specific reasons that you want to install a Nightly build as these builds are meant for experienced testers that know how to deal with issues  ?