Typing them in manually as you visit them should do the trick, but give this thing a whirl (I've never used it, so no idea if it's worth a damn, but it's worth a try):
https://addons.mozilla.org/en-US/firefox/addon/2300
Not sure I'm understanding what you're wanting to do, here. A defragger function simply moves all your data on your disk into a contiguous block that makes access to it easier on the drive's read function. To do that with a Mac, you'll need a third-party utility like Disk Warrior. Honestly, though, the way Mac OS X's file system works doesn't really cause the disk fragmentation issues that Windows does; it still gets fragmentation, but not to any degree near that of an MS OS.
What's more important is opening up Disk Utility (in your >Applications>Utilities folder) and running "Repair Permissions" on your primary drive once in awhile and especially after you install new software. That should help keep your system running smoothly (Onyx is a nice piece of freeware that will do that as well as clean out all your system caches and help optimize your system further; check Versiontracker for the latest version of it). As far as cleaning up unwanted files, there are a few programs out there that will remove remnants left behind by programs you've installed but don't want anymore, but that's about the only kind of file cleanup program I'm aware of. More info on what you're trying to do would help.
jag