User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:57.0) Gecko/20100101 Firefox/57.0 Build ID: 20180103231032 Steps to reproduce: 1. Start FF 2a. Last opened page appears, needs credentials for login -- at the same time -- 2b. FF Sync kicks in 3. I fill in the correct password in topmost prompt 4. I fill in the correct password a 2nd time in the other prompt 5. FF freezes Actual results: 2a. The last opened tabs wants to fill in the login credentials for currently loaded page, thus it needs me to unlock the password manager --> Master-password prompt appears 2b. The FF Sync service kicks in nealy at the same time and also needs me to unlock the password manager --> another Master-password prompt appears on top 3. & 4. I fill in the same password into both prompts consecutively 5. FF freezes, needs to be killed using Taskmanager Expected results: 1. Start FF 2. Firefox prompts only one dialog (for webpage and Sync) 3. I fill in the password only once Or to put it into words: It would be nice if FF only shows the Master password prompt once, even if more than one services (Sync, loaded webpage with login form, ...) require it at the same time.

User Agent Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:59.0) Gecko/20100101 Firefox/59.0 Build ID 20180118012136 I've haven't been able to reproduce the issue you have experienced on the latest Firefox Release 54.0.4 and on the latest Nightly 59.0a1. I've set up a master password, logged into sync, saved a login for facebook, restarted the browser and waited a bit. I've entered the master password twice, for the two dialog boxes, and was able to continue browsing and using the browser as expected. Could you please try to reproduce the issue using a clean new profile (https://goo.gl/AWo6h8), maybe even safe mode (https://goo.gl/AR5o9d), to eliminate custom settings as a possible cause?