When I start my fresh install of odoo 9, the search buttons  (Filters - Group by - Favorites) that should be present below the search field at the top-right of views are not visible. When I inspected the css, I found that the following code block

element {
     display: none;
}

was inserted just before the

.btn-group, .btn-group-vertical { 
    position: relative; 
    display: inline-block; 
    vertical-align: middle;
}

block that corresponds to the styling of the missing buttons. Two colleagues of mine do not have the problem and correctly see the "buttons" while they use exactly the same sources for odoo 9 than me.

Do you have any idea about what could cause the insertion of this annoying piece of code?