In the "Help" menu, the last choice is "Installed Plug-Ins." That will show you what you have now.
I'm not terribly well versed in Safari (I use it solely as my "wide open" browser in private browsing mode, when I have a burning desire to look at some unsanitary website that I just can't get completely whitelisted in Firefox ... which these days more and more e-commerce sites have so many scripts and cross-scripting that that's my only alternative for shopping, but anyway ...)
What adblocker(s) and/or script blocker(s) did you used to use? Adblock Plus, NoScript and Ghostery are the three most popular (though I don't think NoScript has a Safari compatible version)? I'm far from a power user but I can probably give you some pointers on setting up whichever one(s) of those you're used to using?
You can download new extensions at https://extensions.apple.com . I notice there that there's a "Click to Flash" plug-in there, which I'm not familiar with.
Speed comes from what you put behind you. - Judi Ketteler