I have 1password installed on my machine and currently also have it's browser extension for Firefox, I've read that having a browser plugin for a password manager is not a good idea, is this correct?
No, it is not correct. As for everything, it really depends on how they are implemented. Reputable password managers like 1password, lastpass, etc... normally have a quite robust implementation. It's more important to have a solid security strategy behind the lines to avoid/prevent a compromise rather than worrying about it after...
