HOW TO DOWNLOAD FROM NICONICO (with nicozon) IN BROWSER EASY
It works almost like browser youtube downloaders but better.

1. Add a bookmark in your browser with URL being:

javascript:(function(d,j,s){s=d.createElement("script");s.setAttribute("charset","utf-8");s.src=j;d.body.appendChild(s);})(document,"https://www.nicozon.net/js/bookmarklet.js")

2. Find the video you want to download

3. Change your video link format appropriately
(add "ext." before the link and the directory should be "?smXXXXXXXX") like this:

From: https://www.nicovideo.jp/watch/sm123456789
To: https://ext.nicovideo.jp/?sm123456789

4. Click the script you added as a bookmark and wait a bit for the download

5. DONE

For example you want to download
1. You want to download a video under the link https://www.nicovideo.jp/watch/sm18224247
2. You create a bookmark with the above JS (if you haven't already / if you have done it already you skip this step)
3. Fix the link to be https://ext.nicovideo.jp/?sm18224247
4. Click the script bookmark
5. Wait until it downloads

YAY DESU