1. There is a button named library at the top part of your browser, which is referred to as the toolbar. In case you do not see it, kindly locate the menu button, and click it. Then locate library, and click on it. Select bookmarks, and then you will find the "Show all bookmarks" option at the bottom; just click it.
2. Now, on your library window from the toolbar, click import and backup option, then select export bookmarks to html.
3. On this window, select a folder or any location you want to save your file which is named bookmarks.html by default.
4. When you are through with the steps above, click save. Your file would be saved in your selected location, and the window on your Firefox will collect by itself.
At this stage your bookmarks must have been exported successfully from Firefox. You can import them into other browsers if you want.