Firefox makes a copy of your bookmarks the first time you run it each day in a file called something like bookmarks-2012-03-02.json in the bookmarkbackups folder in your Firefox profile. The full path is
C:\Users\<your username>\AppData\Roaming\Mozilla\Firefox\Profiles\<your profilename>\bookmarkbackups\bookmarks-2012-03-02.json
If that folder survived the installation of Windows 8 consumer preview, the 5 latest are still there to import again. Otherwise you only have the latest version on your backup.

And, sorry, I don't know where the Firefox password manager stores passwords and how they are encrypted.

Kees

PS. It makes some sense to install a preview version of a new OS, with all its errors, incompleteness and incompatibilities on a new partition, so the current OS is unchanged and can be used until the final release of Windows 8 comes out in the fall. Seems you didn't do that.