I have created a new profile for Firefox and created the .desktop launcher for this new profile as per this article: How can I use two Firefox profiles?
The launcher works as intended when I left click on it in the Application Display: it launches the specified profile (that I have newly created). But when I add it to Favorites and launch it from the Launcher sidebar, it starts the default profile.
This leads me to believe that the .desktop file is correct but I'm at a loss for this duplicit behavior.