This article is only valid if you are Firefox version 25 or older. Because Firefox usually updates automatically, this article will not apply to most Firefox users.
If you are using an older version of Firefox, you will be prompted to install the legacy Firefox plug-in after you click a computer on your Home page.
When prompted, click the Install Firefox plug-in button.
A new page opens where you will again be prompted to install. Click Install Firefox plug-in now.
If you see a pop-up message "Firefox prevented this site...", click Allow in the pop-up. Download begins.
Once download is complete, the Software Installation window is displayed. Click Install Now.
You will be prompted to restart Firefox. Click Restart Now.
The browser will restart with the installed plug-in. You should be prompted to log in to the host computer (the PC or Mac you are trying to control). If not, return to the page that prompted you to install the plug-in and click Continue (after installation)