Clear the cache and the cookies from sites that cause problems.

"Clear the Cache":

• Firefox > Preferences > Advanced > Network > Offline Storage (Cache): "Clear Now"

"Remove Cookies" from sites causing problems:

• Firefox > Preferences > Privacy > Cookies: "Show Cookies"

If clearing the cookies doesn't help then it is possible that the file cookies.sqlite that stores the cookies is corrupted.
Rename (or delete) cookies.sqlite (cookies.sqlite.old) and delete other present cookie files like cookies.sqlite-journal in the Firefox Profile Folder in case the file cookies.sqlite got corrupted.

• https://support.mozilla.org/kb/Cookies

Thanks cor-el for your very clear directions and suggestions. I followed each recommendation, several times actually and rebooted - no change in firefox behavior. Any other ideas?

I cannot open password protected WordPress pages using Firefox. They open using IE

If I remove the password protection the page opens correctly in FF.

I have cleared the FF cache and cookies several times, No change

I have modified the wp-pass.php file several suggested ways related to the referrer and nothing solves the issue.

I tried:

wp_safe_redirect(wp_get_referer());

to

wp_safe_redirect(wp_get_referer() . '?');

NO GOOD

I tried:

$location = wp_get_referer();
if ( $location == '' )
     $location = './';
wp_redirect($location, $status = 302);

NO GOOD

I have upgraded WordPress to 3.3.1. Still NO GOOD

I have deactivated, and also removed all plug-ins. Still NO GOOD.

Anyone have any ideas?

Why just an FF issue?

IE no problems