Button's aren't available to add to App menu or toolbars, at least with Firefox Developer Edition (v55 x64) with e10s Multi-Process enabled. Installing both the ProfileSwitcher and Profile Folder Button extensions are collectively an alternative that does work with e10s, however.
I haven't tested this, but thanks for making this. I created the addon Profilist - and have linked to this addon from there because users have asked me about a button in the browser to access profiles, I don't have plans for that, so this is a great alternative (if it works).
I just wanted to be able to switch profiles easily. This add-on did the trick perfectly. Once installed I could choose to add any of three button to my toolbar: profile, create profile and switch profile. I added the switch profile and it works perfectly for me. It's free and it works. What more can I say.
the few settings that are there, have no effect, but the real issue being the main reason i installed this was to switch profiles which it fails to do. after reading the description and comparing this to ProfileSwitcher, smaller filesize i thought hmmm maybe this would be a good replacement. nope.