Mozilla has released a new update for Firefox 3.6. Firefox 3.6.9 features 67 bug fixes including patches for 14 security vulnerabilities, 10 of theme labeled as critical.
So you may want to update before even finishing this post: click on the Help menu, and select Check for Updates…
Now that you have updated, Firefox supports X-Frame-Options, a web server directive that tells the browser it should not load a web page if embeded in another one (through a <frame> or <iframe> tag). This will help prevent some kinds of clickjacking attacks.