I know that you can override a style with js but that wont work for me. want to check style for class names being on a white or blacklist and if they contain position:absolut or position:fixed. this works but only for stylesheets that are hosted on the same server because of cross site scripting protection. is there a way to inject the script directly into the css file or to get around this protection mechanism? it also has to work generically on every site.

here is the project: https://github.com/elypter/BlockHead
walking over styles in the stylesheets is currently disabled. you have to change walk_elements to false and walk_styles to true

See @connect metatag for making Cross Site Request using GM_xmlhttpRequest.

https://tampermonkey.net/documentation.php#_connect
-and-
https://tampermonkey.net/documentation.php#GM_xmlhttpRequest

You can check and set any style using jQuery.css()
Please see: http://api.jquery.com/css/