Max says…

I would expect that the Ctrl+Backspace key combination would behave in Firefox as it does in other GTK applications, and indeed Firefox under Win32. The expected behavior is that Ctrl+Backspace will delete one word backwards from the cursor (more specifically it will delete backwards until a punctuation character). However, when I use this combination in the Firefox address bar under Gutsy, the whole URL is deleted. After some digging I came up with a solution: add the following to the bottom of /etc/firefox/pref/firefox.js:

// Make Ctrl+Backspace behave as expected.
pref("layout.word_select.stop_at_punctuation", true);

Hope this helps.