Frequently (but not always), Firefox iOS mobile will startup, allow me to enter a portion of my search text then, open a new tab and/or clear the text I’ve already typed. I looked for settings that would remedy to no avail (“Jump back in” and “start screen” related settings had no affect). Obviously, I’m typing before startup has fully finished, so I’d recommend either delaying my ability to type until startup is finished or addressing the interrupting behavior. For sake of reproducing the error, I tend to fully close apps when I’m not using them, so this is full startup process, not a return to application.