This is the desktop version of Firefox, but with a mobile-friendly configuration. Try zooming and scrolling with your fingers!
Use the official add-on website from Mozilla. Ignore the note about "Add-ons Manager" and hit "Download file" to install add-ons. Take care, some add-ons may not be respectful of your privacy. Here is a free software add-on that we trust:
Read on to set a different homepage, search engine or change other options. Tap the collapsed menu icon on the top right, then select Preferences. Tap the same icon again and decrease the Zoom level to 50%, so the page becomes readable. Next, tap the category of the setting you want to change on the left — house for Homepage, magnifying glass for Search. Finally, change the desired setting on the right.