Firefox Mastery published a nice article about the Firefox add-on Controle de Scripts which lets the user control Javascript events in Firefox. Instead of just disabling Javascript (default Firefox without add-ons), or enabling it on a per-site basis (NoScript) you can configure and control specific Javascripts events.
The two tabs that the extension offers are named Permissions and Popups. The Permission tabs controls Javascript events that move, change, hide or close elements on your screen. You can for example deny Javascript the right to close Windows that were not opened by them or to hide the status bar or scroll bars.
The Popup tabs require knowledge of Javascript events or a Google search if you do not know Javascript. You can select the Javascript events that are allowed to trigger a popup. While we probably all know what the events click and dlbclick do we might have difficulties with mouseup or change.
A excellent Firefox add-on that should be implemented as standard in Firefox 3.
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Using javascript to hide and unhide elements dynamically
this extension is identical to JavaScript Options: http://www.oxymoronical.com/web/firefox/jsoptions