Firefox Search Engines post 35.0.1
Have you upgraded to Firefox 35 or above? Find loads of unwelcome search engines in place of your original chosen engine?
Me too! Downright annoying isn't it? I prefer Google UK, especially being based in the UK, but the Google search engine provided was Google US (ie: .com not .co.uk). There is no obvious way to restore Google UK as a search engine option.
The solution is to Left click on the Search Engine icon (or magnifying glass at the left of the search box) and choose Manage Search...