Today, when I was searching for a Mozilla plugin I came across this plugin FlashBlock, which blocks Flash, Shockwave and Authorware contents in a web page, when using Mozilla. It then leaves a placeholder on the page that allows you to click to view the Flash content.
This is the description of the plugin as found on mozdev.org :
Flashblock is an extension for the Mozilla and Firefox browsers that takes a pessimistic approach to dealing with Macromedia Flash content on a webpage and blocks ALL Flash content from loading. It then leaves a placeholder on the page that allows you to click to view the Flash content.
Note the word "pessimistic" in the content ;)
You can view some screenshots of how the blocked contents would appear, here. Once you install the plugin the blocked contents show up as a placeholder with the flash player icon in it and whne you roll over it it changes into a Play icon.