Well thank you. I'm, however, not looking for recommendations - I'm looking for technical answers. When you install Rally and subsequently join a particular study, you are asked by the extension to agree to allow certain access. For at least two Rally clients, this request includes "Access your data for all websites" which includes user names and passwords. Since I am uncomfortable giving this access even to the most trusted of Mozilla Rally clients, I won't do it.

So then I see there are Profiles and I think I can create a new profile and then use Rally. So now with a little background I will restate the original question:

If I create a new profile and sign in to it with my default profile's login, will the new profile expose details of login information etc. from my default profile? Or, is it necessary to create a new Firefox account for my new profile? This seems to completely defeat the convenience of using profiles. I hope that clears up my question.

Thank you.

If you sign in to a Firefox Account that you also use for other profiles then this profile will automatically have all the logins stored on the Sync server from that other profile. Only if you do not connect to Sync and do not have passwords store in the Password Manager (about:logins) then you can be sure that Rally can't access any logins (passwords).

That's what I was looking for. Thank you.