Till now whichever Firefox version –Nightly, developer, beta and stable –you install first on your computer Firefox uses that profile for other Firefox installations, this to change however from Firefox 67 onwards. Mozilla has decided to use dedicated profiles per installation beginning with Firefox 67 Nightly on January 28, 2019. The beta, release, and ESR will also have separate profiles when version 67 reaches release.
The company has favored dedicated profiles per install over the channel. On January 28, Firefox starts creating dedicated profiles for each Nightly installation and Nightly from on that date won’t share its profile with other Firefox versions installed on your computer.
The bug mentions the details about the profile-per-install plan “We use a dedicated profile for a each install of Firefox on the system as identified by a hash of the installation directory. In order to identify which install to give current profile to we look in compatibility.ini to see which install has launched the profile. Other installs receive a new profile.”
The advantage with this if you’ve different Firefox installations, you can switch between them and run them at the same time.
If you’ve already created a separate profile for Firefox, you won’t notice a change with this development.
If you want your Firefox profile data to be same for all Firefox installations, then you need to use Firefox account to sync them.