I think the 'gMsgCompose has no properties' error is from something else; that occurs when you close the window.
I didn't get that, but I did get the NS_ERROR_INVALID_POINTER problem when trying to Edit As New into a cached compose window. No error appears in the Error Console if you try to Edit As New into a new compose window.
Also, that error only occurs (in my early testing, at least) when the cached compose window is plain text. If it's HTML, I only see the messagebox with "Error creating compose window" in it.
I think the 'gMsgCompose has no properties' error is from something else; that occurs when you close the window.
I didn't get that, but I did get the NS_ERROR_ INVALID_ POINTER problem when trying to Edit As New into a cached compose window. No error appears in the Error Console if you try to Edit As New into a new compose window.
Also, that error only occurs (in my early testing, at least) when the cached compose window is plain text. If it's HTML, I only see the messagebox with "Error creating compose window" in it.