Safari does not recognize flash plug-in and will not play flash video

Question

I use Safari as my go-to browser for web sites that would otherwise require me to turn off my several ad-block/flash-block plugIns for Firefox.  I do have it set to ask for permission ('Trust this site?') for every time I use flash on a new site (since I reset Safari regularly and clear all cookies every time I close it this means every time, every site, it asks).  New problem started sometime in the past week:  Safari is returning a 'download flash' icon on some videos on some web sites--but on others it correctly goes through the 'trust this site to use flash?' routine and when I click 'trust now' it plays the video normally.  Trying to figure out if this is a Safari problem, flash problem, or web site problem.  How can Safari both recognize that flash is being asked for (that's why it shows me the 'download flash now' icon, right?) and not recognize that it has flash installed?
Safari Version 7.0.4 (9537.76.4)

Answer 1

If you're sure you've installed the latest version of Flash, 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
and click Delete All. 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
If you get a warning of a "blocked" or "outdated" plug-in, then from the menu bar select
 ▹ System Preferences… ▹ Flash Player ▹ Advanced
and click Check Now. Quit and relaunch the browser.
If the warning persists, 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.