The reinstall might just have worked! *fingers crossed*
Here's what I did, fwiw.
Exported bookmarks, uninstalled firefox, deleted all user data and the FF folder itself.
Uninstalled Combofix.
Restarted, just in case.
Redownloaded FF and tested google by reopening browser and searching and clicking the first link 3 separate times (it seems like the 3rd search always brings the redirect).