The "developer edition" is a special version of the Mozilla Firefox web browser tailored for web developers. It has features stabilized in nightly builds, provides experimental developer tools, and it is configured for development, so some options as remote debugging, are enabled by default.
The ln -s command to link the ~/.local/opt/firefox to ~/.local/bin/firefox-dev gives the error “No such file or directory”
EDIT
For some reason, after executing touch firefox-dev in /bin and then trying to create the link it gave me “File already exists” THEN after deleting the file and trying it once more, it worked! But still not quite as intended, on further inspection I noticed there egdoc is missing from my ubuntu install.
When you create a symlink from ~/.local/opt/firefox to ~/.local/bin/firefox-dev you must be sure that the ~/.local/bin directory exists and create it if it doesn’t. It is possible that you receive the “No such file or directory” error because of that (it would be very strange, however, since unless you installed a very minimal system the directory should exist).
Please notice that the tutorial is meant to show how to install firefox developer edition for the specific user and not system-wide, so the /bin directory you mention is never involved. It would be very strange to find the egdoc directory on your system, since it is the home directory of the user I used in the article.
You should write [Desktop Entry] at the beginning of the file firefox-dev.desktop in the part Creating a desktop launcher
thanks, worked for me. 