How To Download And Set Up Firefox Quantum On Debian Stretch
Download Firefox Quantum
Anyway there is a solution to that, open gedit text editor and copy the below texts:
Save the file as firefox-quantum.desktop to .local/share/applications/ directory. If hidden folders do not appear visible on save dialog box, press CTRL+H to make them visible. Once saved to the desired directory, hit the same key combination i.e., CTRL+H to make hidden folders and files invisible.