On Windows, the Flash player plugin DLL is under C:\Windows. When everything is working correctly, Firefox finds the Flash player by checking entries under a registry key. I don't know whether this check takes place every time Firefox restarts, or at other intervals.

Other plugins may install differently, e.g., copying a DLL into a folder under c:\Program Files (x86). It's rare for a plugin to be profile-specific.

If your plugin list is not updating, the pluginreg.dat file that stores plugin information might be corrupted. This article has a section on how to delete that file so Firefox will regenerate it: https://support.mozilla.org/en-US/kb/troubleshoot-issues-with-plugins-fix.... Does that help?

I agree that it is rare for a plugin to be profile specific. What I see however is that one profile does have Flash and several other plugins whereas the other profile does not.

Removing the plugin DB for regeneration is described in many articles but was no help. Uninstalling Flash was the easiest to test. I uninstalls correctly from profile 1 (not present in profile 2). When reinstalling it, it again appears only in profile 1 and not in profile 2.

Creating a new profile 3, imports all Plugins like in Profile 1.

I can create additional profiles but I want to understand what is happening to Profile 2.

There is a preference you can toggle in about:config to prevent Firefox from checking the Windows registry for plugins. By default, this is true but setting it to false will cause Firefox not to pick up Flash and other plugins that advertise their availability in the registry: plugin.scan.plid.all Could you check for that?

The plugin.scan.plid.all was set to false -- changing it back to true solved the issue.

TNX !