I have the same issue. My Firefox is v3.6.6 (just updated yesterday) and the uploader doesnt react to any click on the InsertButton now. Upgrading to some sort of version of Silverlight isn't really an option to fix this since we have a lot of anonymous users we don't know. I hope you can find out whats going wrong in this process and that you can update the ajaxuploader to support both previous versions as the current firefox version.