Thank you for your feedback! This extension uses your default search engine, you can easily change it to your preferred one in Firefox settings. Here's how: https://support.mozilla.org/en-US/kb/change-your-default-search-settings-firefox
If you'd like to add or remove search engines, you can find instructions here: https://support.mozilla.org/en-US/kb/add-or-remove-search-engine-firefox