I have used Video DownloadHelper 4.6.4 firefox plugin for this post. But any firefox plugin can be installed with similar steps.

PART I – Installing (2 Methods)

METHOD (1) – “Add to Firefox” – STEPS for installing the plugin directly on firefox:

Step 1. Open Firefox Add-ons website by following this link: Video DownloadHelper 4.6.4. Make sure this website is open with firefox browser.

Video DownloadHelper 4.6.4 Firefox Plugin

Step 2. On the plugin web page you will see a green button named “Add to Firefox”. Click on that button.

Add to firefox button

Step 3. The “Software Installation” window appears. Click “Install Now” button.

Firefox Plugin Software Installation Window

Step 4. The video download helper starts to download. Wait till the download finishes in few seconds.

Video DownloadHelper downloading

METHOD (2) – “Download the .xpi file” – STEPS for downloading the plugin as a .xpi file and installing:
Step 1 . Open Firefox Add-ons website by following this link: Video DownloadHelper 4.6.4. Make sure this website is open with any other browser than firefox.

Video DownloadHelper 4.6.4 Firefox Plugin on non firefox browsers

Step 2. On the plugin web page you will see a green button named “Download Now”. Click on that button.

Download Now Firefox Plugin Button

Step 3. Save the “downloadhelper-4.6.4-fx.xpi” file somewhere on your computer. You will need this file to do the installation later.

Step 4. Open a blank Firefox browser window.

Step 5. Drag to Firefox window, the “downloadhelper-4.6.4-fx.xpi” file that you had downloaded in step 3

Step 6. The “Software Installation” window appears. Click “Install Now” button.

Firefox Plugin Software Offline xpi Installation Window

PART II – Restarting and finalizing installation

Step 1. Click “Restart Firefox” button to finish the installation and restart firefox.

Restart Firefox after plugin installation

Step 2. If the following window shows up click “Restart” button.

Restart Firefox restore tabs

Step 3. Firefox closes itself. Wait till firefox restarts on its own. When Firefox loads again, the plugin should be installed and ready to use (If the Add-ons window appears, just close it) .

A – HOW TO DOWNLOAD AND INSTALL Video DownloadHelper 4.6.4 firefox plugin:

Video DownloadHelper 4.6.4 is available here.

If you don’t know how to install it, please read my post on How to install firefox plugins

B – HOW TO USE Video DownloadHelper 4.6.4 firefox plugin to download any youtube video as .flv or .mp4 video file:

Step 1. Open a youtube video. I’m opening the following url for this example: 1,000,000 Subscribers!!!

Step 2. Click the down arrow next to DownloadHelper Icon on firefox toolbar. It should look something like the snapshot below. Basically you need to select the type of video that is available for download and click “Download” on the menu.

Video DownloadHelper Download Menu

Step 3. Select the folder where you want to save the video and click save. The video file will be saved in the folder that you selected. Enjoy the video!

DONE!

If you don’t know how to play .flv files you might want to try this free flv player: Applian Technologies FLV Player FREE

There is also another method to download youtube videos: How to download youtube videos using keepvid.com