On Windows, your profile folders are under %APPDATA%\Mozilla\Firefox (and that folder contains .ini files pointing Firefox to your profile folder(s)). The LocalAppData path has caches and other stuff that isn't important.

Is sync being enabled/disabled or connected/disconnected the only change from week to week? If other data/settings are lost, that might reveal a pattern that would provide a clue to what is changing.

This is definitely good information, thank you. The behavior I am experiencing would be consistent with profiles.ini being missing (although it is present): Firefox starts up with no connected profiles or addons. Both the old profiles directories and profiles.ini are present. Could file permissions have any bearing on this behavior?

I assume (haha) that file permissions follow your network/domain login rather than an idiosyncratic local user identity, but I don't really know.

After Firefox starts up without knowledge of your previous settings, can you reconnect with your data using the:

Profile Manager Page

Inside Firefox, type or paste about:profiles in the address bar and press Enter/Return to load it.

This page should list at least one profile and could list many. (Each profile has two folders and one or more buttons. Do not use any Remove buttons!)

The profile that Firefox is currently using (the one that lacks your data) will have this:

This is the profile in use and it cannot be deleted.

Do you have any other profile(s) listed on this page? These should populate from the profiles.ini file.

If so, you can check whether one of those is your recent profile by clicking its Launch profile in new browser button.

If it isn't what you want, simply close that new window.

If it IS what you want, back on the about:profiles page, click the Set as default profile button for that profile so Firefox uses it automatically at the next startup.

If your recent profile isn't listed on the page, hmm, maybe profiles.ini got cleared/reset?

I believe that you are correct - profiles.ini may be cleared, reset, or is otherwise out of sync, which would be a Windows/administrative policy issue.

Following the steps you provided and comparing them against Profiles/, I see one more profile in the directory than what is listed in about:profiles. That missing directory is not as a value in profiles.ini. By replacing one of the other profile entries where name=dev-edition-default with the name of this folder and restarting Firefox I successfully loaded the profile.

This certainly solves my issues relative to Firefox. I now need to diagnose what in the administrative policy causes profiles.ini to fall out of sync.

@jscher2000 - you rock! Thank you for your help.

Note that you can use the Profile Manager to register an orphaned profile .

You can recover an unregistered profile via these steps:

• use the Profile Manager to create a new profile
  https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles
• click "Choose Folder" in the Profile Manager
• browse to the location of this profile to register this profile in the Profile Manager and use this profile

See "Profile was moved or renamed":

• https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

Note you should never use "Choose Folder" to specify a folder that already contains files and that isn't a Firefox profile folder. Only use "Choose Folder" to recover an profile that isn't listed in the Profile Manager.