If you have downloaded a .xpi driver or another extension for testing, you can install it into your browser manually or via automation: Where can I found FirefoxDriver XPI? · Issue #199 - GitHub
Because this is a legacy component, you will not find it as a standalone download on the primary Mozilla Firefox website . Instead, it is usually retrieved from one of the following locations: firefoxdriver.xpi download
Some legacy wrapper projects, such as SeleniumBasic , maintain archives that include these files for older browser support. How to Install an .xpi File in Firefox If you have downloaded a