I find it so annoying to open a tab and have a web page suddenly blare out this sound from video.
I often right click and open link in new tab. I’m still reading the first news article when that sound from that other article I sent to a new tab suddenly slaps me in the face.
Can I block auto play scripts on web pages? Maybe with Firefox settings or if necessary, grease monkey?
I use “notscripts” in chrome, and firefox has “noscript” which will block most, if not all of that kind of stuff. If you’re comfortable with extensions, use it 
I think it’s great.
Uninstalling Flash is another option. I use Safari without Flash for most browsing. Almost all sites work fine, the most annoying ads go away, and YouTube still plays videos.
On the rare occasions I need to use a site that’s accessible only with Flash, I use Chrome. It has a built-in Flash engine, so there’s no need to have the Adobe Flash player installed.
You can turn easily turn off Flash in Firefox. Just choose “Add-ons” from the menu, and scroll down to “Shockwave Flash.” Click on “Disable.” That will take care of a lot of videos.
Opera has an “Enable sound in web pages” option under Settings > Quick Preferences. If you use Opera you could try de-selecting that to see if it helps. You can also de-select “enable plug-ins” to disable Flash.
Edited to add - Three people with three different ways to get rid of Flash. We should start a Flash haters club.
I use an add-on named FlashBlock. It stops autoplay but puts a > button on the flash content so you can play it if you want.
I tried disabling flash and that fixed it. No annoying auto play video. But, that means turning Flash back on when needed.
Flashblock sounds like a good solution too. I need to give it a try.
I use Flashblock (in Firefox) too. Mostly I am pretty satisfied with it, but on some sites (notably Slate.com) it does not work for some reason. I contacted the makers of Flashblock about it, and tehy agreed that it is a problem, but did not suggest or promise any solution. (However, Slate generally just has animated Flash ads, not videos).
Also, although most videos currently rely on Flash, a few use Java and will still play despite Flashblock. As HTML5 begins to spread, though, we will probably be seeing less and less reliance on Flash.
With Flashblock, Flash videos come up as an open box, and you have to click inside them to start the video playing. No need to disable or re-enable Flash in your browser. That is probably just what you want.
Surfing the new would be really annoying if not for Flashblock. QAdblock, NoScript, etc.!
That’s it. I’m never flashing again.
For those sites that Flashblock breaks, you can always right-click on the button and enable Flash for this site. Or you can add the toolbar button, and then use it to disable Flash when you need it.
BTW, the problem arises on pages that use invisible Flash to do things other than playing animations or movies. If the Flash is invisible, there’s no place to put the button. For example, I don’t know if it’s still the case, but Comedy Central used to require Flash to be enabled in order for you to leave a comment.
If you have Adblock installed, click options and uncheck, “Show tabs in flash and java”. That will solve most of your problems, IME. What remains is the sidebar thingy. I haven’t seen that lately: I’m not sure how I got rid of it. But recently I added Easylist to my Adblock options. Which is a shame really: I don’t mind ads as long as they are unobtrusive. I suspect Easylist blocks some stuff that I wouldn’t mind viewing.