Setting a master password breaks several things
I have set a master password to protect my stored passwords, bug since then, I encounter two main problems.
First one, I have a corporate proxy with authentication. When master password is set, when starting Firefox, I get the master password prompt. After typing it, the page won't load, the authentication to the proxy isn't done and no proxy authentication dialog popup. I have tried to toggle the key network.automatic-ntlm-auth.allow-proxies in about:config between true/false without success.
The other problem is when displaying store credentials (about:logins). You should type your master password, but then, the page displays no stored password. Waiting a bit (2-3 minutes) make them appear, but there is no loading indication and the browser becomes largely unresponsive surely due to the cost of password deciphering (I have a lot of stored passwords, around 700…).
I haven't found any bug declared for those two problems.