Frankly I am tired of the Flash based image uploader. It doesn't work most of the time, when it works it is pretty unstable, frequently fails on Opera, doesn't work (for me) on Firefox in Linux even with latest Flash, doesn't work with .htaccess fix and more. In short it is simply not worth it. You are much better off without the Flash based image / media uploader in WordPress 2.5.1. There is a simple way you can disable it and forget it.

1. Download the no flash plugin and upload it to your wp-content/plugins folder.

2. Activate the plugin from Plugin Management screen

That's it. No more checking Flash version, no more modifying .htaccess and tearing your hairs in frustration when WordPress Image Uploader fails to do its simple job - upload image!

Now that you have disabled it, you have to first browse the file and then click on upload to upload it, the traditional html way to upload files.

Having said that, if you really love pain and frustration then you may try some of the fixes mentioned here, none of which incidentally worked on any of my blogs.