it seems that upgrading to firefox 12 has many problem. Most of the people have problem after upgrading firefox 12. Most of the time the upgrade from firefox 11 to 12 not successful.so the problem has occure. I recommend u to download Firefox 12 from mozilla.org and install it. It is the easiest way to solve ur problem. There are many other ways to solve the problem.but the easiest way is this

first,uninstall ur firefox. Then download a newer version of firefox from mozilla.org install it.and browse. I hope ur problem solve,if nt,just leave a reply

Uninstalling & reinstalling FF 12 made no difference. The master password dialog is STILL popping up inconsistently.

r u tried to open the site in firefox safe mood? Try it and say me the result

Dude, opening a site is not the issue. It's the master password dialog that doesn't always pop-up like it's supposed to even when opening a site with a stored password. I think it's a bug in Firefox 12.

yes.firefox 12 is full of bugs.

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.org/kb/Safe+Mode

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Makes no difference. The Master Password dialog does not show up. I can go to a page that requires a password (like Gmail) and still no prompt for master password. ISometimes I can hit 2 or even 3 sites (all that require passwords) before the MP dialog shows. Even if I start to enter the name and password, the dialog STILL doesn't show. f I hit refresh on the page, then the MP dialog will usually show up.

For now I'm just going to disable the feature.