Right-click in the URL bar.
Click on 'Edit search engines...' when the context menu appears.
Click the 'ADD' button in the bottom right-hand corner.
Enter the following details:
Search engine: SiteSearchr.com
Keyword: *
URL with %s in place of query: https://sitesearchr.com/search?q=%s
Scroll through the list of search engines until you find our listing for SiteSearchr.com, then click 'Make default'.