It’s good to use both Firefox and Chrome to test out what your site will look like, even if you prefer just using one browser most of the time.
Visual Studio Code: https://code.visualstudio.com/
GIMP (to make graphics for your site): https://www.gimp.org/
GIMP is kind of like Photoshop, except that it’s free. The name sounds a little questionable, but it stands for the GNU Image Manipulation Program.
Online tools for checking your code for errors and warnings:
HTML validator: https://validator.w3.org/