I stumbled across this and its been driving me crazy for Months. Firefox developers seem to have made a mistake in one of the tools or scripts that sets the default permissions for a page in a [non-intuitive] way. "Extremely Non-Intuitive" I suspect its in the silly Popup about "Stop Script" that is like a EULA it's so long, and no one ever reads. The Permissions page for a site is separate from the Tools>Addons> Ask, Never Activate, whatever Blizzard of useless settings for "protecting people from plugins" Even if FireFox is totally up to date. Even if Flash Shockwave, Director, whatever is totally up to date. The "PAGE" Permissions has an entirely separate "disable plugins" page... attached to the Site, and clearing the Cache [Does Not Clear the Permissions] for the Site, and it does not appear in the about:config or about:anything pages that I have seen. Its actually more refined and easier to understand, but you have to navigate to the page [Per Site] (while its Flickering and Reloading the Continuinlly crashing webpage.. or worse alternating between multiple pages crashing and cycling) and manage to right click and choose "View Page Info" then click on the Apple Inc. Icon for "Settings" labeled "Permissions" at the top of the page that Pops up. A Whole new list of "Activate Plugins" will appear with a differently worded set of "Activate" questions 1. Use Default 2. Always Ask 3. Allow 4. Block Whats more it appears if its been accidentally set.. its kept across Updates, and "Inherits" through any page linked from a page that is "blocking" a plugin.