I am running WP 3.0.1 on a self hosted server - doing this for 3 years now.
Recently, when I want to add an image, the AJAX popup does not appear, but instead, the browser (Chrome/Safari/FF on a Mac) asks me if it is ok to switch to a different site. When I agree JUST the media uploader itself is opened fullscreen in the browser window and I can upload pictures. However, this hinders me from actually adding the pictures to the post.. since the actual post is gone and replaced by the media upload window..
Hard to explain.. the media uploader does not load in a java popup above the edit post site, but instead in a full frame with its own URL.
I have deactivated all plugins, tried different browsers and emptied my cache... any ideas?