Have you considered connecting both Nightly and Firefox 87 to the same Firefox Account and using Sync for this data exchange? How do I set up Sync on my computer?

Otherwise...

Regular Firefox and Nightly use different profile folders. Because Nightly is two versions later, it may not give you stable results to force Firefox 87 to use it. There is a method for that if you want to try it toward the end of the following article: Dedicated profiles per Firefox installation.

Otherwise, you could migrate key data files from your Nightly profile folder to your regular release profile folder. This article has more info on those: Recovering important data from an old profile.

I would advise against trying to use the Nightly profile with release at this will likely break storage (Nightly uses LSNG) and possibly other components that are using newer schemes, o best is to use Sync or if possible use export/import if possible (bookmarks, logins, tabs).