This tool will help you to create a Firefox profile with the defaults you like.
You select which features you want to enable and disable and in the end you get a download link for a zip-file with your profile template. You can for example disable some functions, which send data to Mozilla and Google, or disable several annoying Firefox functions like Mozilla Hello or the Pocket integration.
Each Setting has a short explanation and for the non obvious settings links to resources describing the feature and the possible problems with it.