A list of Gecko configuration options (accessible by entering about:config in any Gecko-enabled browser, such as Firefox) can be found in the knowledge base (via linmagazine).

I'll be listing interesting options here whenever I find them.

editor.singleLine.pasteNewlines	Integer	Determines the behavior when pasting content containing newlines into single-line text boxes. 0: Paste content intact (include newlines) 1 (default): Paste the content only up to (but not including) the first newline 2: Replace each newline with a space 3: Remove all newlines from content 4: Substitute commas for newlines in text box
browser.urlbar.autoFill	Boolean	True: Enables inline autocomplete. False (default): Opposite of above.