I am using Firefox for android on Android 4.1.2, and I created a master password for passwords etc on Firefox, and promptly forgot it.
I think a way to solve this and start again is to remove the profile's directory (according to this, it is located at
data/data/org.mozilla.firefox/files/mozilla/), but as I have not rooted this device, that is difficult.
I have also tried removing
/storage/sdcard0/Android/data/org.mozilla.firefox, which did not work