Non-breaking space 0xa0 character prevents Confluence page edit in Firefox

Steps to replicate:

1. Create a new page with the following content (or attachment from CONF-22110):

     --script=SCRIPT       script of actions, or a lua script. We assume a  lua
                           script if the file ends with .lua
   
   

2. Save the page and re-edit in Firefox to see the warning
   
   

After minification is disabled, debug shows this line:

return (text || "").replace( rtrim, "" );

This only affects Firefox and to some extent other browsers. As described by Bob McChesney:

Firefox 3.6/4.0: Editor opens but is empty and it is not possible to switch to preview or source.
IE 9.0: [Seperate to this issue, it seems that rich text editing is broken in IE9. (Blocks are not shown and carriage returns do not behave as expected.)] Not possible to switch to markup or preview.
Chrome: Chrome is fine, so that's my workaround. I note that it is quite slow though, indicating that possibly there's an exception being handled?

Other symptoms:

• If editing using Rich Text Editor, the content of the page will disappear. Clicking on save or cancel will not modify the content.
• If editing in wiki markup, the same warning will be shown in Firefox. But the page will be editable (and save-able) and the content will not disappear.