Salve! I, too, am very interested in this. I use two firefox profiles - one for browsing and one for development. And I use the addon called "ProfileSwitcher" in both profiles. What that does is that it always pops up firefox's "choose profile" dialog that asks me which profile I want to launch. It also gives me a toolbar button to allow me to launch another profile - but it doesn't do anything at all about which instance is the "default browser".
Now, whichever profile I launch FIRST on the system - that one will be the default "Firefox". And if you go to settings and tell ANY Firefox instance to check whether it is the default browser, each and every one will say that it is already default. The system's "default browser" is only for the browser, not the instance.
This may be a useful link for this thread
as it refers to some registry settings.
So I would like to choose which instance of Firefox is the "default browser" via this nice Browser Tray Switch.
I created a thread for this at SuperUser
. We'll see if anyone comes up with an answer!
[I originally posted here
, but nobody ever answered... I guess the thread was too old].
Also, it seems that the "default instance" is controlled by Firefox in Application Data\Firefox\profiles.ini. There is an ini entry there for "default=1". Problem is that you seem to have to restart all instances of Firefox...