At regular intervals, Google Chrome will prompt to make it the default browser if it is not. This can be annoying if you are using Chrome but do not want it to be the default browser. Unfortunately, this behaviour cannot be turned off via the settings, but fortunately, it can be turned off via a manual edit of a configuration file.

Open Finder, from the menu select Go → Go to folder, and past the following path:~/Library/Application Support/Google/Chrome/Default

Find and open the Preferences file with your favourite editor (such as TextEdit).

In the file, search for the text:"browser":{Replace it with:"browser":{"check_default_browser":false,Don't forget  ...