There's a bug in Firefox 32, that some tabs miss the favicons: https://bugzilla.mozilla.org/show_bug.cgi?id=1061456
The bug is caused by the introduction of the new cache and shows up in case pref "browser.cache.disk.enable" is set to "0" and "browser.cache.disk.smart_size.enabled" set to "false".
IIRC, the portable container for firefox sets those values forcefully, that's why I'm writing this here.
The bug seems to be gone if pref "browser.cache.disk.enable" is set to "false", so it would be nice if FirefoxPortable container would forcefully assign that value to that pref.