On Linux Mint, the default version of Firefox is installed and configured to allow the following search engines to be queried directly from the address bar:
- Yahoo!
- Startpage
- DuckDuckGo
- Wikipedia
Mint defines these as the default available set of search engines based upon 3 criteria (funding to Linux Mint, privacy support and whether the search engine is non-commercial).
Other search engines such as Google, Bing or Twitter, etc. can easily be added into the default version of Firefox however.
To add a different search provider, browse to Search Engines
At the bottom of the page, click on the icon of the requested search engine, then click on the ... button in the URL bar and select the Add Search Engine option.
You then have the option to change the default search engine within Firefox preferences to your new choice.