transfer passwords to Firefox

Yes, Keychain Access is useable when browsing with Firefox. In the Firefox security settings there is an option to have Firefox remember passwords and autofill them -- however you will have to remember to keep both lists updated if you make changes in either!

It helps to have keychain access in the dock so it can opened it quickly.

It never occurred to me to password protect a browser, they don't contain any actual data, just pointers (addresses) to sites and maybe to HTML files and images.

What exactly is your goal?