@JessTheUnstill hmmm. It can also happen that the fork gets so popular that almost all users switch to it, leaving the original project without a meaningful user base, see for example OpenOffice vs. LibreOffice.
Another possibility that has happened: the original project resolves its leadership issues, and the fork gets re-merged. As I understood, this happened in OpenWRT vs. LEDE.
But I don't think one of those will happen to Firefox, based on Mozilla's current power in leadership.