Why does Firefox add hide some images?

Question

css

There is, for example, such html markup

<a href="">
<div class="div1">
    <img src="img2" alt=""/>
</div>
</a>
<a href="">
<div class="div2">
    <img src="img2" alt=""/>
</div>
</a>

In Firefox and only .. in the browser console, you can see the following code

img[src="img1"] {
    display: none !important;
}

why does he add it? what's wrong ?