Favicons are the little icons that appear on each tab in your browser. Although they can help you find which site you have opened in a given tab, when you have a lot of tabs opened, they can really, really annoy you if the site designers have decided that a blinking favicon is the way to go. That is why, Firefox allows users to disable favicons in a rather easy way.
Open Firefox and enter about:config in the address bar. Firefox will warn you that you can really mess things up if you are not careful.
Click the I’ll be careful, I promise! button and the configurations will open:
In the Filter textbox enter browser.chrome.favicons:
Double click on the browser.chrome.favicons preference to set its value to false:
Do absolutely the same for the browser.chrome.site_icons preference:
Restart Firefox and you are done.