Hi PedroFerrari, there are many possible places for YouTube to appear, so I'm not sure what you mean by "as an app".

For example:

(1) You can bookmark YouTube and have it displayed on the Bookmarks Toolbar. This article has more information on bookmarks: Bookmarks Toolbar - Display your favorite websites at the top of the Firefox window.

(2) You can "pin" an open YouTube tab, which shows the tab differently, only as an icon. This article has more information on application tabs: Pinned Tabs - keep favorite websites open and just a click away.

(3) Some home pages -- the content area below the toolbars -- may allow you to add a thumbnail image of a site for quick access. This would depend on what site or add-on you are using to generate your home page.

Are any of those what you're looking for?

By the way, the Question Details > More System Information for your post shows out-of-date versions of the Adobe Acrobat plugin (which is part of Adobe Reader) and the Flash player plugin. I'm not sure whether that information is accurate but for security reasons, you should update.

For Adobe Acrobat, you can use the Help menu inside Adobe Reader to Check for Updates, and after you update Reader, it will point Firefox to the latest plugin automatically.

For Flash, you can get the current version on this page:

https://www.adobe.com/products/flashplayer/distribution3.html

In the first table, look for the row for "plugin-based browsers" and you can use either the EXE or the MSI installer for Windows.

If you are using such an old version to avoid problems with Flash, this is some standard guidance that addresses the most common issues with the Flash Player plugin. I'm sure you've seen some of it before, but just in case:

(1) If you have any recorders/downloaders that interact with Flash media make sure they are as up-to-date as possible, or disable them temporarily.

(2) Disable hardware acceleration in Flash: right-click the media in the player and choose Settings, then the first mini-tab and uncheck the box to use hardware acceleration.

More information in this support article from Adobe: http://helpx.adobe.com/flash-player/kb/video-playback-issues.html#main_Solve_video_playback_issues

(3) Disable protected mode (Windows Vista and higher)

The protected mode feature of the Flash player plugin has security benefits, but seems to have compatibility issues on some systems. You can disable it using the Add-ons page. Either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Plugins. On the right side, find "Shockwave Flash" and click the More link. Then uncheck the box for "Enable Adobe Flash protected mode" and try that for a day to see whether it helps.