I've renamed the .mozilla folder as suggested, and so far it seems to have worked.
Presumably it is now safe to delete the renamed folder, but I'll wait a while before doing that.
The only thing I did differently that day was to let a friend show me one of his favourite sites. Presumably that was where I acquired the infection. The site was called something like "Mami's s**t", which doesn't sound very wholesome anyway.
I certainly won't be going there again.
I won't mark this thread as "Solved" for a few days until I'm certain the hijacker is gone, and I'll be following the discussion in the hope of learning more about this particular item of malware.