Yes but what FF says after installation or update?
It mentions to don't forget to install or update your flash for the browser to work correctly!
If you can believe it. So I think browser vendors also have responsibility for this. They don't mention the risks to the end user.
btw there are many addons for FF to surf safely, haven't tried flashblock but I use noscript and I can selectively run them. Betterprivacy will clear them on demand or browser exit, but it checks the default flash folders.
And flash is not specific to html5. What they say is correct and is just one of the applications with LSO.