Working with text editors in Mac OS

Make sure that you save the file with .html extension (like index.html). TextEdit might automatically save files by adding a .txt extension. Then browsers will not open it as an html file, but as a text file. To see what your extension really is CTRL + click on the file then select get info - under the general section  it should say Kind: HTML document.

If despite your attempts to save as html it adds a .txt extension (as .html.txt)
then go in finder and change the extension to html.

For more info on working with HTML files in textedit you can see http://computers.tutsplus.com/tutorials/quick-tip-configure-textedit-for-coding-html--mac-44786

Another possible source of problems is described in http://www.askdavetaylor.com/how_do_i_save_html_files_from_textedit/

Some people say that TextWrangle works better for them...