you'd have to disable javascript - but this won't be a very practical solution since many sites are broken without it. you can use an extension like [https://addons.mozilla.org/de/firefox/addon/noscript/ noscript] & do a whitelist approach - disable js by default and only allow it on sites that you trust/need. here's some more stuff that websites can find out about you: [http://browserspy.dk]

so there isn't a easy way to hide my resolution using javascript.