Summarize this article:

It's an app icon that resembles an orange fox wrapped around a blue globe. This menu item is either in the upper-left side of the browser window (Windows) or in the left side of the menu bar at the top of the screen (Mac). A drop-down menu will appear. If you don't see this option on a Windows computer, press the Alt key first. It's at the top of the drop-down menu. This will open the Firefox bookmarks manager. This option is near the top of the bookmarks manager. Clicking it prompts a drop-down menu. You'll see this option near the middle of the drop-down menu. A new window will appear. In the window, check one of the following boxes:   Microsoft Edge - Import bookmarks directly from Microsoft Edge (Windows only).  Microsoft Internet Explorer - Import bookmarks directly from Internet Explorer (Windows only).  Chrome - Import bookmarks directly from Google Chrome.  Safari - Import bookmarks directly from Safari (Mac only). If you don't see your preferred browser here, click Cancel, click Import and Backup again, and click Import Bookmarks from HTML... instead. It's in the bottom-right side of the window. If you're importing a file instead of browser data, go to the file's location and click the file to select it. Check the boxes next to all items that you want to import from the other browser (e.g., Favorites, Cookies, etc.). If you're importing a file, skip this step. It's in the bottom-right corner of the window. Doing so signifies that the bookmarks have been imported into your Firefox browser. If you're importing a file, click Open to upload the file to Firefox. This will import all of the entailed bookmarks automatically.

Summary:
Open Firefox. Click Bookmarks. Click Show All Bookmarks. Click Import and Backup. Click Import Data from Another Browser…. Select a browser. Click Next. Select items to import, then click Next. Click Finish.