Using the Firefox, SeaMonkey, or Flock browsers, it is possible to perform a web search just by entering your search term into the Location Bar and hitting “enter.”
By default, these browsers use Google, but you can easily change it to StartPage. Here’s how:

*NOTE: Please make sure to follow the below directions exactly, as changing the “about:config” preferences can influence the behavior of your browser negatively.

Type ‘about:config’ in the browser location bar and hit ‘enter’
Accept the warning message to be careful
Enter ‘keyword.URL’ in the filter on top of the page
Double-click on the ‘keyword.URL’- line that shows up
In the pop-up window replace the Google string with: https://startpage.com/do/search?language=english&cat=web&query=
(For mobile version please use: https://startpage.com/do/m/mobilesearch?language=english&cat=web&query=)
Click on ‘OK’
Close the window or tab