Refine AllowMultipleInstances support?

Hi John! Thanks for your excellent work, as always....

I have a conundrum. Right now, AllowMultipleInstances=false in FirefoxPortable.ini means two different things at once:

1. External invocations of Firefox, e.g. from a system-installed copy, will instead open new tabs/windows in Firefox Portable so long as Firefox Portable stays running;

2. If another version of Firefox, portable or not, is currently open, Mozilla Firefox Portable Edition will refuse to start.

I really want the behavior of (1), but do not want (2), as I have one Portable copy for normal browsing (AllowMultipleInstances=false), and another for testing work (AllowMultipleInstances=true).

Now, if I were to start up the system-installed Firefox when the testbed browser is already running, then the system-installed version does actually start and work properly. If I try to start the Portable intended for normal browsing (AllowMultipleInstances=false), it sees the testbed one running and refuses to start.

Perhaps there's a way to change this to detect when a globally accessible Firefox is running? That way, "isolated" instances (AllowMultipleInstances=true) would stay isolated, but they would not prevent a non-isolated Portable instance from starting up.