You don’t need to download Firefox again—changing your Firefox Account password doesn’t affect the installation. If Firefox “went away,” it may just not be pinned to your taskbar or desktop yet. Search for **Firefox** in the Windows Start menu; if it opens, you’re all set. To make it your default browser, go to **Settings → Apps → Default Apps**, choose **Firefox**, and set it as default for web browsing. If Firefox truly isn’t installed, simply download it again—it won’t hurt anything and only takes a moment.