Best would be to move the entire profile folder to that other drive (i.e. use the Profile Manager to create a new profile and transfer personal data to the new profile). On Linux you might be able to create a symlink, but storage is very complicated and easily gets broken so best is to keep the profile in one location. Note that if you create a new profile this way that the disk cache and other temporary data stored in the secondary location will be stored in the same location.

You need to create a new folder on the other drive to be used for the profile that is exclusively used for the profile (no other files present) beforehand and use the "Choose folder" button to select this folder.

• https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles

Moving the profile directory is pointless bc I want the profile directory to be without these storage files when I create a backup of it. For the moment I found a way to achieve that with the command rm -rfv ~/.mozilla/firefox/[profilename].default-release/storage/default/https* but hopefully some day the developers will make a way to change the location of the storage. It would be better if they moved it to ~/.cache.