Polluting simple web page

When have the extension enabled it pollutes a web page looking like this:

```
<!DOCTYPE html>
<html>
    <head>
        <title>title</title>
    </head>
    <body>
        Text
    </body>
</html>
```

to this:

```
<html>
    <head>
        <title>title</title>
    </head>
    <body>
        <pre>
           Text
	</pre>
    </body>
</html>
```