Plug-ins in bowser helps to imitate quick actions for performing particular tasks. On Safari browser if you talk about plug-ins you can see which ones are installed and control when websites are allowed to use these plug-ins on the Safari browser.
Actually, to load content rich web pages faster, save time and bowser more securely Safari browser is optimized for contents that use the HTML5 web standard, as this browser always prefer contents while loading the web pages.
Many websites require plug-ins like Java or Flash to view the media contents like animation, video, or other proprietary content. You can install such plug-ins, and then run Safari browser to turn them on for the web pages you are likely to visit. After turning-on the plug-in, it will remain active for long as you regularly use that plug-in on any of the website.
When you visit a website that needs plug-in to show the media contents, you might see a placeholder where that content will be visible. At this moment placeholder might show the plug-in is missing, that you need to click to use the plug-in that might be blocked, or outdated.
If the plug-in is installed on your browser, Safari might ask whether to use the plug-in once or every time you visit this particular site. Here you need to get in touch with Apple safari technical support for temporarily allowing plug-in to view contents on Safari.
To allow or block websites from using plug-ins you need to go to the preferences, and open security. First turn-off all the plug-ins for all websites uncheck allow plug-ins, however few websites that require a plug-in might be not functioning properly or showing the placeholder instead of the plug-in content or might ask you to install the plug-in in the safari browser.
If you want to view the plug-ins or turn off a specific plug-in for all websites, you need to click the plug-in setting button, which should be deselect the checkbox for that plug-in. Conversely, you can also configure a plug-in for specific websites, whether or not the website presently requires the plug-in for your Safari browser. Here you can also take Apple safari help to deal with such issues and solve the plug-in related various issues on Safari browser.