Firefox users can open profile folder in a number of ways. For example, typing %APPDATA%\Mozilla\Firefox\Profiles\ in the Run dialog should display a list of all profile folders that you’ve created, or you can press Alt + H, select Troubleshooting Information and click the Show Folder button. You can also place the folder button right inside the hamburger menu and even add it to the main toolbar.
To add the button within the hamburger menu or the toolbar, you can use Profile Folder Button 1.0.5 (13.4KB) or Open Profile Folder 22.214.171.124 (7.2KB). The latter also lets you open the current profile folder from the Tools menu.
After the installation, restart the browser.
Drag and drop the button from the Customize page to the toolbar or the hamburger menu area.