This feature actually is long overdue, a substantial amount of Firefox crashes are indeed caused by Flash failing and Mozilla’s competitors (MS IE, Apple Safari and Google Chrome) already have similar (or even more exhaustive) crash-protection.
Once you’ve installed Lorentz (or Chrome or IE8 or Safari off course) you can safely visit http://flashcrash.dempsky.org/, which exploits a bug that was reported 19 months ago and which may still cause the most recent Flash-version (10.0.45.2) to crash. And if flashcrash doesn’t bring up the plugin-crash-dialog, you can always kill the “mozilla-runtime” process that hosts the plugins, just for kicks!
looks like flash-crash-protection will be in the upcoming 3.6.4, i upgraded to the first beta last night. the “mozilla-runtime” process has now been renamed, look for “plugin-container” in your process-list.