if you drag a photo from windows explorer and drop it into an open canvas (blank file? not sure what to call this) in photoshop, it will import the image but it put it in transform mode and resize it so that the image's width matches the current files width.
however if you do the same, if you drag an image from firefox into the same open file in photoshop, it will not resize the image and put it into transform mode. i really like the resize preference as it makes things very convenient. is there an option to enable this resizing for dragging and dropping images from a web browser?