Avoid injecting same style sheet twice

[mjethani]

Background

Consider this document:

<style>
div {
  color: red;
}
</style>
<div id="price">0.9109041176174169</div>
<script>
setInterval(() =>
{         
  document.getElementById("price").textContent = Math.random();
},
1000);
</script>

And this filter: 127.0.0.1#?#:-abp-properties(color: red)

On Firefox this causes the same style sheet to be injected every one second. Since this is not allowed on Firefox, tabs.insertCSS throws. It is allowed on Chrome though (I implemented it), and Chrome will just insert a duplicate style sheet. Subsequent calls to tabs.removeCSS will then only remove the last matching style sheet.

The correct thing to do here is to make sure we don't inject the same style sheet twice.

Also see #6458.

What to change

In lib/content/elemHideEmulation.js, do not add the exact same list of selectors twice.

Resolution

See #6504. We no longer use style sheets for any element hiding emulation filters (not even :-abp-properties()).

[mjethani]

Second attempt at fixing this: patch ​#29728690

[mjethani]

This should be fixed in core.