Welcome to WebmasterWorld Guest from 188.8.131.52
Safe mode solves it, so must be a misbehaving extension, argh.
UPDATE - PROBLEM SOLVED:
One of the default rules in ADBLOCK PLUS [forums.mozillazine.org] extension was mucking with Google.
Forgot I had upgraded it recently and just had to take out the filter rule.
Thanks for the feedback, it helped diagnose this very quickly.