INSTALLATION AND CONFIGURATION
Prepare Opera for NotScripts by opening Opera’s configuration editor (opera:config) and in the Persistent Storage section set the value “User JS Storage Quota” to at least 5000. Press “Save”. Restart Opera, then install the extension.
Once installed, press the NotScripts button in the address bar (usually in the upper right corner of the browser) and press “Options” to set desired options. The default setting of “Whitelist”, which I prefer, provides highest security: it blocks all scripts not specifically authorized. A reasonable “set and forget” configuration to protect naïve end users from themselves is Whitelist + Same Origin (SO).
If you use NotScripts in its most secure whitelist mode, you will find that Facebook scripts are an all-or-nothing affair: either you block Facebook scripts (making that site unusable) or you allow them (including on third-party sites, allowing Facebook to track you). To get around this, Facebook users will want to install Facebook Blocker. It allows you to block Facebook scripts from running while on third party sites. When you’re on Facebook itself, scripts run fine if they are allowed in NotScripts.
If you uninstall NotScripts later, consider returning User JS Storage Quota to its default value of 0.
ALTERNATIVES TO NOTSCRIPTS
I haven’t tried it, but a number of former NotScript users frustrated with its recent lack of development have moved on to Scriptweeder.
These notes refer to NotScripts 1.1.0 on Opera 12.11 and were last updated 15 December 2012.