I can reproduce the error in the demo page.  I edited the page. Submitted the content. hit the back button and tried to edit the content again but it was read only and there were errors on commands.

 

Here is some more details about the platforms and browsers: 

Issue Description:

Rich text editor defaults to readonly and throws command errors when used in Firefox 1.0

This occurs after the second load of an editor.

 

Tested Platforms and Browsers:

 

Macintosh 10.3

• Firefox 1.0 – ISSUE CONFIRMED
• Firefox 1.5 – could not repeat issue
• Firefox 2.0 – could not repeat issue
• Safari 1.3 – could not repeat issue

 

Macintosh 10.4

• Firefox 1.0 – ISSUE CONFIRMED
• Firefox 1.5 – could not repeat issue
• Firefox 2.0 – could not repeat issue
• Safari 2.0 – could not repeat issue

 

Known Resolutions:

• Shut down all instances of the current browser and open up a new browser session and edit content until issue occurs.
• Upgrade browser to a more recent version.