Better link
http://www-archive.mozilla.org/unix/customizing.html#keys
sounds like
cmd_beginLine cmd_endLine
are what you need to modify in the example given
<binding id="editorUser">
<handlers>
<handler event="keypress" key="w" modifiers="control"
command="cmd_deleteWordBackward"/>
</handlers>
</binding>
I havn't used it but this claims it will change the Firefox behaviour as well (specifically make them behave like windows for the home and end keys)
https://addons.mozilla.org/en-US/firefox/addon/keyfixer/
I think cmd-left and cmd-right are used by Firefox for " back" and "forward" so those never work on Firefox (unless perhaps you go find where Firefox specifies its key bindings and change them)