Signal protocol supports multi-device when the device is capable of storing the keys (like the Signal desktop app). His point about web browsers still stands I

Signal protocol supports multi-device when the device is capable of storing the keys (like the Signal desktop app). His point about web browsers still stands I believe. Although you could use local storage, you would have to do that with every browser you logged into and also somehow make it user-account-specific. I definitely see the challenges there for them. What would you think about using a user's password to encrypt the browser keys and store them on Facebook's servers? Is that too large a compromise for usability?