Add --depth=1 if you aren’t sure you want to bother with all the commits yet. May want it for actual development so you have change history.)
In the project folder, run ./bootstrap.sh
Before opening the Xcode project, open firefox-ios/Client/Configuration/Fennec.xcconfig and change MOZ_BUNDLE_ID to a different bundle under a domain you control. For example, I have com.codingitwrong so I used com.codingitwrong.Fennec
Open firefox-ios/Client.xcodeproj in Xcode
Choose the Fennec scheme (Firefox will be harder to set up as it has a custom-set provisioning profile)
Go through each of the Targets, making sure “Fennec” is selected across the top. Fix anything marked in red:
Team should be changed to your Apple Developer account
App Groups should be changed to a group specific to you. You can add a group. prefix on the MOZ_BUNDLE_ID you used previously
Try to run on your phone. If you get any other errors with identifiers, fix them one at a time