I use the appimage, but just now when trying to install the deb, saw that i have that, too. (the browser ext. said I was using an outdated version and I was). I have the most popular FF extension for it, KeePassXc-Browser. I can see the KeePass symbol by the login and can see that I manually entered that login, password, URL in a group name in my .kdbx file. But, when I click on the logo in the login in area, it still makes me type in both login and password. Also, I am rather confused about how to organize (if I need to) my groups (I use 4 IDs online) since I use 2 PCs and the browser extension asked me to enter a title for each PC used. I am still not sure if everyone needs to use that extension, but it seems the only way.
I began by using one file for each ID, then when that didn't seem to work well, i went to one master file with 4 groups.
Also, it seems the file may time out periodically and need to be reopened - that is what the browser extension seems to say. That means shutting down the app on my PC and logging into it again - almost as annoying as logging into each site - depending on how often I change sites, I guess.