I know in the past, password managers built into certain web browsers were stored in plain text (and maybe still are! I am unsure), which is, to say the least, a problem. However, from what I can see on my preferred browser Firefox, it seems to be encrypted. With Firefox Sync, they’re synced (sunc?) across my devices, can be locked by a master password, and generates strong random passwords.
Compared to Bitwarden, which I purchased on recommendation from Security Now’s Steve Gibson, and to support the companies that support TWiT (plus, I don’t mean to brag, but I can afford $10 a year), Bitwarden has a few extra additions like safely storing card information, identification information, other notes, and second factor authentication.
Aside from the card and identification information that doesn’t seem to be encrypted in Firefox, it seems both Firefox and Bitwarden safely store passwords, offer a master password lock, and generate random passwords. Firefox is also extremely cross platform so it’s everywhere like Bitwarden. Just out of curiousity, am I missing something or are these both good ways to manage passwords?
If you needed dental work, would you go to a dentist, or would trust aunt Betty’s neighbours friend who is “just as good”? I think being a specialist in something probably gives Bitwarden that extra little boost in credibility. (Of course one might have said that about LastPass at one time, so who really knows.)
For a browser, it is a “nice little extra”, for the password manager, it is what they do. As @PHolder says, they are specialists, they know what they are doing.
Also, password manager works pretty much everywhere. I use 1Password and have it on all devices, even if I am not using Firefox (my main browser on desktop, but not on mobile). It also fills in in apps, it stores my non-website passwords as well as my ssh keys etc.
If you use Firefox everywhere and don’t need passwords outside of the browser, they are better than nothing, but password security isn’t their day job. Also, if you switch browsers at some point, you need to be able to get them all into the new browser.
E.g. I use Firefox first on Windows, Mac and Linux, but I also use Edge and Brave on Windows and Safari on macOS as secondary browsers / for specific tasks - E.g. Edge for managing our M365 instance at work. On mobile I use Safari.
If there is a problem with one browser on a particular site, or there is a security vulnerability that is being actively exploited, I can switch without thinking to a backup browser.