I'm not sure how it goes for anyone else, but when I was trying to figure out how to get worlddownloader to work for 1.8 I had alot of trouble finding which downloads and files were compatible. So I figure I might aswell make a quick tutorial with the links I managed to find for anyone else who is struggling. 

1) This is LiteLoader
2) This is the lightloader mod
3) Download both of these and run the LiteLoader installer
4) Load the minecraft client, check your profiles, if the installer worked there should be a profile labled something alone the lines of 'liteloader 1.8' Select that and run the client.



5) After running the profile close it and go to your .minecraft folder.
6) There should be a 'mods' folder and subsequently a '1.8' folder inside of the mods folder.
7) Drag and drop the worlddownloader mod into that 1.8 folder then load the client again.
8) If all is well you should now have a "Download this world" button in the options screen!

Hope this helps!