Starting with v59, Firefox for Android is now an Assist App. This means you can start a web search by holding down the home button on your device, if you set Firefox as your default assistant.

How to change your Firefox homepage using the home button One way to change the home page is to use the home button. The home button does not appear in Firefox by default, so here's how to add it: ...

Firefox: Usable Home Button transforms the “Home” button in Firefox to a quick button that takes you to the homepage of any website you’re visiting. So for example, if you were reading this ...