Disabling loading specific JavaScript files with Firefox
Several options:
Use the Addon "Adblock Plus". It will probably still accesses the js but does not execute it.
Use the Addon "Greasemonkey", which - when cofigured right - does not even touch the js-url. But its generally harder to configure right. ;)
Have a look at Firefox's buildin security policies: http://kb.mozillazine.org/Security_Policies Here you can block javascript on an url or even function-level
Go to your hosts file C:\Windows\System32\drivers\etc (Windows) or /etc/hosts (Linux).
Add:
127.0.0.1 ajax.googleapis.com (separated by a tab)
And reopen your browser This way the jQuery file will fail to load.