This is a broad statement and I’ll allow that the Firefox manager is not as bad IF setup correctly. But I imagine that your laptop at some point in its life will have opportunities for someone other than you to access it and with the password manager get access to all your secure sites, like your bank.
I obsess over how long I allow the password manager to fill in sites before I need to re-enter my master password. I do fast mental math on probability based upon people and location. At home, 2 hours is good. Melanie Pinola from Lifehacker has the details if you want to dig into them. Otherwise just get a Lastpass account.