The Internet Explorer uses favicon.ico for his favorites.
The Firefox browser uses favicon.ico for his tabs.
If you don't specify a favicon URL on a page, the Firefox browser automatically downloads
http://yourSiteUrl/favicon.ico and because of this fact the JSpider have to do the same.
You will find more information with a search engine by searching for favicon.ico.
Thank you for JSpider and for reading this.
I hope, you will support favicon.ico soon.