James, you've opened up an interesting thread of ideas.
Regarding security -
1. It isn't integrated with browsers (no automatic fill-in-the-blank), but to address your 'too many for pencil and paper' scenario, here are some ideas (practicality aside).
Put your multitude of passwords into a file.
a) Use Windows' Encrypting File System (medium format must be NTFS). For information, see Help.
- To set: in Explorer, right-click on file or folder > Properties > (tab) General > (button) Advanced.
- Usage is transparent for 'your' logon ID. Any other user logon (including an administrator) gets 'Access is denied' message. Copy password from file, Paste into browser password field. (Hacker protection, but not theft protection if thief can log on. Power-on and Logon passwords will alleviate this.)
b) Store the file on a removable medium: diskette(?!), USB drive, ... . Device is not shared. Then mount it only when needed and Copy/Paste. Cumbersome.
c) Even more secure and cumbersome: Combine a) and b). But remember NTFS prerequisite.
2. Haven't tried this, so experiment with appropriate archive/backup -
- Similar to 1.a - Forget the Firefox Master Password; but set Encryption on the signons.sqlite file.
Note that (1) is general, not Firefox specific. The methodology in (2) is general, but details are browser-specific, depending upon how/where internal passwords are stored.
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.12) Gecko/20101026 Firefox/3.6.12 (.NET CLR 3.5.30729)