Since at latest the 4/1 Serpent 55 release (may be older but I haven't tested older releases): on the about:profiles page, if you try to use any of the "Launch Profile in new browser" buttons, they don't launch the selected profile. They all launch the default profile instead. Thus, to switch profiles on Serpent 55 you much change the default profile, restart, then repeat the process if you want to go back to your original default profile.
The latest Serpent 52 doesn't have this bug; the "Launch Profile in new browser" buttons work correctly there.
roytam1
commented
2 years ago
Since at latest the 4/1 Serpent 55 release (may be older but I haven't tested older releases): on the about:profiles page, if you try to use any of the "Launch Profile in new browser" buttons, they don't launch the selected profile. They all launch the default profile instead. Thus, to switch profiles on Serpent 55 you much change the default profile, restart, then repeat the process if you want to go back to your original default profile.
The latest Serpent 52 doesn't have this bug; the "Launch Profile in new browser" buttons work correctly there.