[Firefox] Set SearX as Default Search Engine

Step 1: Choose your searX instance here

Step 2: Visit that webpage, and click your page actions, select “Add Search Engine”

Step 3: Navigate to your Browser Preferences, choose the Search tab on the left, under the drop down for Default Search Engine choose searX.

Step 4: Additionally you can uncheck / remove any search engines you do not want to use under the One-Click Search Engines area.

Sources: OpenSearch Mozilla