Though I somewhat alluded to the issue, an important aspect of using any password manager, be it software or pen and paper based, is that you'll need to input the sign-in credentials at some point in your browser. If your system is infected with malware, both ways can result in your credentials being stolen. Whether imputing via a hardware or software based keyboard.
You should routinely make sure your system is clean of any such malware, especially keyloggers. Which have the entry point to many of the recent credit breaches in the news. As they can be difficult to detect.
Malwarebytes Free is an excellent tool to do so. In fact, the only app that was able to detect my test keylogging malware.
Another is to use a keyboard encryption app as part of a layered security plan. I found these to be effective in blocking captured data, so long as they loaded ahead of a keylogger. If not, the malware could take control of the clipboard, and render it pretty much useless.