where does `resource://gre/res/html.css` come from?

I'm just using ASP.NET MVC 2 and realized that I get a ghost stylesheet

And I can't get ride of it...

Biggest problem is that on other browser I do get the same behavior with this ghost CSS, and it's driving me crazy!

On the image above I'm using Firefox 3.6.11 with Firebug 1.5.4

I have this html.css file nowhere in my Visual Studio Solution, how can I get ride of it as it's screwing my design with it's line 345

ul, menu, dir {
    display:block;
    list-style-type:disc;
    margin-bottom:1em;
    margin-left:0;
    margin-right:0;
    margin-top:1em;
    paddi开发者_开发百科ng-left-ltr-source:logical;
    padding-right-rtl-source:logical;
    padding-start-value:40px;
}

C:\Program Files\Mozilla Firefox\res\html.css is the location of the css.

Nowadays, with Firefox v68, forms.css is located in : "c:\Program Files\Mozilla Firefox\omni.ja\chrome\toolkit\res\forms.css" where omni.ja is a ZIP archive.