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I'm also using the Koivi editor with both Firefox and Internet Explorer. I'm very happy with it.
The only thing that it is missing is the ability to upload files. I'm pretty sure SPAW can do this and I've heard that the latest version of SPAW does support Firefox but I'm not technical enough to download it from their site without the great step-by-step instructions usually provided on this site.
So... I really like Koivi because it supports Image Manager and Firefox. But no file upload option.
In my perfect world I would be able to work on an article, and click on an upload button, locate the file on my hard drive, click upload, have the editor recognize the file type and place the appropriate icon into the page I'm editing with a link to the file I just uploaded.