For those trying out Firefox 5.0 (in the Mozilla Repository for 11.4) and looking for KDE Wallet integration add-on, you can download it from Firefox addon for kwallet KDE-Apps.org.
It was updated to ver 0.9 on June 27, 2011; it does not yet show in the Firefox search for Add-ins.
I have FF 4.0.1 here, the one that comes with openSUSE 11.4. It should be integrated with KDE. My openSUSE before this was 11.2 and I used Konqureor there, which of course was (and still is) integrated with Kwallet. My FF 4.0.1 on 11.4 isn’t. Is that something I missed or is this what you point to something new with FF 5.0?