I downloaded a new version of Java to day (both 32 and 64 bite)
And it does not work with Firefox 18.
I have tried manuel instalation but no.
oracle made an error in registring the java plugin for mozilla-based browsers in version 7u10 & 7u11... this will apparently just be fixed with its next release.
for a workaround see http://kb.mozillazine.org/Java#Add_back_missing_registry_key