I see frequent posts about the "master password" popup problem many, including myself, have wrestled with after installing the new SeaMonkey 2.0. This post is intended to try to help resolve this issue.
The most likely fix is to type "about: config" in the address field, and, after accepting the warning about being careful, scroll down to the line, "signon.startup.prompt;false" and double click it, if it says "true" to make it say "false."
However, for many, this does NOT fix the problem, especially if you've been using SeaMonkey for some time, and have never set a master password. This was the case for me. After several attempts, and reverting back to V 1.18, I finally stumbled on an answer that fixed it for me.
In your home directory, look for the hidden folder, ~/.gnome2/keyrings. Delete everything inside the ~/.gnome2/keyrings folder;
****CAUTION**** Be extremely careful when using this command. You can cause severe, and probably irreversible damage to your machine.
$ rm -rfvd ~/.gnome2/keyrings/*
A safer approach might be to open your file browser, click on View > Show hidden files, then navigate to /home/you/.gnome2/keyrings, and then delete your files. At least then, if you've made a mistake, you can retrieve them from the trash.
Either way, you will need to close all programs, and either log out, or reboot your system.
Then, when you launch SeaMonkey, the keyrings will be re-written in that folder, and that annoying "master password" pop-up will not appear.
I hope this helps.
Thanks,
owa