WYSWIWYG editors have been requested but probably won’t ever come standard, as they’d bloat the system out and/or make it more than one file, sort of defeating the novelty. Plus, if you’re working in PHP or non-HTML code, they're generally more hindrance than anything else.
Just because I don't want to do it, though, doesn't mean it's impossible. About halfway through, look for this line (If you're searching for it, it's the second instance):
// EDITThis is the edit page code. Its textareas can be modified to work with whatever editor you like. If the editor is initiated via jQuery, you can call it in the jQ code in the footer.
Syntax highlighting is more likely to come in future versions... as long as it doesn't make the script too big.
Because "OneFileFileManagerTextEditor" doesn't quite have the same ring to it, duh.
Maybe later!
The reason there isn't default support for multiple users is that all of their info will have to be stored together, more or less in plain text, at the top of onefilecms.php. Giving people different usernames and passwords then is sort of futile, since everyone who can log in can view onefilecms's source and config variables. (This answer kind of ignores MD5 hashes but is valid for most considerations.)
It isn't entirely necessary, but it does nice little progressive enhancements like warn if you try to leave w/o saving and stuff like that. Feel free to take it out if you're trying to trim down your figure.