It should be OK, outside of any malware at work(you judge). If you've recently installed Firefox or upgraded, that should display. Visiting websites that should be more active or animation may also need some plug-in ie: Flash player or Adobe needs. Click on the link/button should provide what it needs or recommends. Just going to the Firefox website itself and check the plug-ins that may interest you is another "tweeking/fine tune" of Firefox. I find the most demanding plug-in is Flash player, so if it needs that, go ahead and get it. Anything else is up to you.
I use Windows XP with Firefox.
On most sites, in the area where a pop-up has been prevented from opening, I am getting this message: Additional plug-ins are required to display all the media on this page.
On the right-hand side, in a rectangular shaped box is: Install Missing Plugins...
Is this a legitimate window?
Will I be safe in installing the plug-in?
I don't have any idea for what they are used.
Thanks for any help out there - but in plain language, please.