file called f.txt.js automatically downloads using safari

Hello,

I'm using 13 inch macbook pro late 2013 running yosemite, and I've run into a very strange problem since yesterday. Seems as though when I open a youtube video from safari, it automatically downloads a file called f.txt.js to my downloads. I have no idea what this file does, or why it keeps automatically downloading.

Strangely, when I use chrome to open the same video, this doesn't happen.

I checked and I have no safari extensions. I also used clamxav to check if there was any malware in downloads, but it didn't catch anything.

I'd really appreciate a help on this. Thank you!