Issues Downloading Youtube vids in safari

Here's what I'm doing :

while video is open
window ->
activity ->
find largest file.. usually several mb
click file
check downloads

Before, the file would be automatically named get-video or something and I could click and play the file instantly.

Now the file in downloads is named videoplayback.download and is nothing but a bunch of code when opened.

I tried changing the extension to .avi, but then it just says this is not a movie file.

any tips?

Edit...

I added the extension .flv and it works!

But why am I having to do this? hmmm