How Flash destroys your browser's performance. That's any browser, any performance, any day of the week. It's sad, really. Was Flash ever usable? I've only been online since 2004 so I don't remember it being a huge problem until say, maybe 2007-2008ish, but before that, most people's connections to the Web were so slow that as a fairly considerate website owner, you wouldn't - as a matter of course - display Flash to them on a regular basis, anyhow.
I've disabled Flash so many hundreds of times over the years in every version of Windows, from XP right through Windows 10, over "Shockwave Flash script running slowly - stop script/wait" messages, and had so many browser and individual tab crashes over the years because of Flash, that as a matter of routine over the last few years I either disable Flash altogether or force-kill it through Task Manager as needed, which is almost every damn time I browse. It's a crippling, far-from-secure, ridiculous plugin and in all the years it's been around, I wish any competitor would have replaced it with better technology.
Speaking of which: Silverlight, HTML5 (YouTube reverts to HTML5 by default for users who watch video on a fresh browser install that's still lacking Flash; there's also an alternate YouTube which plays nothing but HTML5 videos) and...? Why, in all these years, has no viable alternative become a more widespread and popular choice so we can finally kick Flash to the curb?