I'm giving it 5 stars, but with two minor crits.
One: you don't include sync.com as one of your cloud providers, which, given that they're probably one of the most secure options available (even they can't access your data) is a shame. I keep my kdbx file in my sync box, but I was still able to add it as a valid option by using the "local file" option. (Like most cloud options, they provide local file access).
And, having added that and my keyfiles, and entered the master password, I duly went hunting for a trial site to test it on. This is where you scored big time. I have been a Keefox user for a couple of years. Up until firefox went quantum and keefox went bananas and ditched the most important functionality in their plugin. I refer to the ability to use the extension simultaneously as bookmark database AND autofill ("Find and Fill" functionality).
If I want to login to one of my email accounts, I just want to type in email and get a reasonably short list of contenders, click on the one that matters, get taken to its login page and have the username and password fields completed automatically. Keefox stopped doing that and made it clear that they weren't even going to try to find a way to do it which would be compatible with the new Firefox environment. Their ludicrous suggestion was that I bookmark the relevant password protected sites. (I have over 800)
But you've done it. And what you've sacrificed to make that possible is entirely rational and makes much more sense than what they've done.
Setting up the username and password for an account is something you (generally) only do once for a given account. But you might visit that account thousands of times. Which would you rather lose - the automatic capture of credentials (a one off) or the automatic "find and fill" option which you'll need forever? It's a bleedin nobrainer!
The second criticism actually cost you a star, until I figured out my mistake and edited this review. You need to make the "remember" option slightly more obviously relevant to the PASSWORD DATABASE. I looked at it and ignored it, (assumed it was site specific instead of relating to the password file) after "find and fill" on my first test site. Went to another and the sodding password file was locked. That was because I'd left the "remember option" on "don't remember" instead of my preference (remember until browser exit).
Otherwise thumbs up
2 observations after a couple of days using it:
1 Displaying the Keyfile name is almost as bad as displaying the password in plaintext. Strongly suggest you hide that.
2 Can we have a way to store preferences (like the "Remember" option above)