Why am I seeing blocked plug-in where short videos are?

Question

When I click on a video on Facebook a small box says Blocked Plug-in.  I am unable to view the video.  How can I change this?

Answer 1

If you can't install or update Flash, follow these instructions.
If you have installed the latest version of Flash, please take each of the following steps that you haven't already tried. After each step, relaunch Safari and test. For a "missing plug-in" error, start with Step 8. Back up all data before making any changes.
Step 1
You might have to log out or restart the computer before a Flash update takes effect.
Step 2
From the Safari menu bar, select
          Safari ▹ Preferences... ▹ Privacy ▹ Remove All Website Data...
and confirm. Close the window. Then select
           ▹ System Preferences… ▹ Flash Player ▹ Advanced ▹ Delete All...
In the sheet that opens, check the box marked
          Delete All Site Data and Settings
then click Delete Data. Close the preference pane.
Step 3
If you're only having trouble with YouTube videos, log in to YouTube and load this page. You may see a link with the text "Leave the HTML5 Trial." If so, click that link.
Step 4
a. If you get a warning of a "blocked" or "outdated" plug-in, then select the Security tab in the Safari preferences window. In the list of plugins on the left, there should be one—and only one—entry for "Adobe Flash Player," showing the same version number that you installed. Select that entry. On the right there will be a list of websites for which you have specifically allowed Flash, if any. It's normal for the list to be empty. Below that is a menu labeled
          When visiting other websites
From that menu, select either Allow or Ask.
b. If you still get the alerts, then go back to the Flash Player preference pane and select the Advanced tab. Click Check Now. Quit and relaunch the browser.
c. If the alerts still persist, triple-click anywhere in the line below on this page to select it:
/System/Library/CoreServices/CoreTypes.bundle/Contents/Resources
Right-click or control-click the highlighted text and select
          Services ▹ Open
from the contextual menu.* A folder should open. Inside it, there should be a file named "XProtect.meta.plist". If that file is missing and you know why it's missing, restore it from a backup or copy it from another Mac running the same version of OS X. Otherwise, reinstall OS X.
*If you don't see the contextual menu item, copy the selected text to the Clipboard by pressing the key combination command-C. In the Finder, select
          Go ▹ Go to Folder...
from the menu bar and paste into the box that opens by pressing command-V. You won't see what you pasted because a line break is included. Press return.
Step 5
In the Safari preferences window, select the Advanced tab and uncheck the box marked
          Stop plug-ins to save power
Step 6
Open this folder as in Step 4:
/Library/Internet Plug-Ins
Delete the following item, or anything with a similar name, if present:
          Flash Player (failing).plugin
You may be prompted for your login password.
Step 7
Re-download and reinstall Flash. Download it from the domain "get.adobe.com". Don't click a link from any other website, including this one, because you can't trust links. They may be an attempt to trick you into installing malware masquerading as Flash. Type the address into the browser window. Never download a Flash update from anywhere else.
Step 8
If you get a "missing plug-in" error, select
          Safari ▹ Preferences... ▹ Security
from the Safari menu bar and check the box marked 
          Allow (or Enable) plug-ins
Then click the button marked
          Manage Website Settings...
if present and make sure that the website is not blocked for Flash.
Step 9
Select
          Safari ▹ Preferences... ▹ Extensions
from the Safari menu bar. If any extensions are installed, disable them.