Appeared on the site this , what is it?

Question

css

What is the reason? 
In their place there were icons and buttons forward back at the slider.
In firefox, that icon is everywhere, and in Chrome, the slider shows the correct icon, and in other places it is just empty, that is, without .
The cache is not configured. No work has been done.

В стилях эти иконки которые пропали выводятся так:
например content: \f003 
то есть Font Icons

другая была в стилях как
font-family: 'icomoon';
content: attr(data-icon);
speak: none;
font-weight: normal;
-webkit-font-smoothing: antialiased;
content: "\e00d";

Answer 1

So you can’t say right away, you have to look, probably just the picture didn’t load, or you deleted the icons.

Answer 2

For a serious answer, you must specify the address of the site in the question.
And as a hypothesis, check where the jQuery library comes from. The jQuery site was hacked.