How can I set the country used by the search bar?

I want to be able to set the search engine used by the search bar to a country-specific one, which may not be the country that I'm in. Normally I use google.com.au and bing.com.au. If I'm in France on holiday, I still want to search using google.com.au and bing.com.au rather than letting Google auto-detect that I'm in France and turn everything into French. How can I manually set the URL used for the search engine to force it to use the Australia-specific one all the time, no matter where I am? A similar situation occurs if I'm using a VPN; just because the VPN says that I'm in Germany doesn't mean that I want German results. Just give me google.com.au and bing.com.au that return Australian results no matter where I'm located! In Chrome it's easy (because you can just modify the search string to add ".au" to the end), but I haven't found a way to do it in Firefox.