May I suggest that Firefox should delay syncing the Master Password until the first time that it is actually required, even if syncing is turned on?
If you use Data Syncing then this is attempted every time you start Firefox. If you also use a Master Password then it tries to sync your passwords every time you start Firefox too. This means that every time you start Firefox it asks you for the Master Password. This is incredibly irritating.
I realize that you need to sync at the beginning of a new session but would it be possible to delay the syncing of passwords until the user actually needs to use a password (i.e. the default behavior for using a Master Password without syncing). After all, it doesn't matter if the passwords are not synchronized if they are not being used. When a password is actually required then Master Password could be requested and the stored passwords could be synchronized if the correct Master Password is supplied.
Re: May I suggest that Firefox should delay syncing the Master Password until the first time that it is actually required, even if syncing is turned on?
The people who answer questions here, for the most part, are other Firefox users volunteering their time (like me), not Mozilla employees or Firefox developers.
If you want to leave feedback for Firefox developers, you can go to the Firefox Help menu and select Submit Feedback... or use this link. (You'll need to be on the latest version of Firefox to submit feedback). Your feedback gets collected at http://input.mozilla.org/, where a team of people read it and gather data about the most common issues.
You can also file a bug report at bugzilla.mozilla.org regarding the Master Password prompt at Firefox startup when Sync is on. However, see this "WONTFIX" bug (and any other bugs that come up during the bug-filing process) before doing so:
Bug 675883 - When sync is on, and there's a master password, the master password dialogue keep popping up