See:

• http://en.wikipedia.org/wiki/Character_encoding

The selected encoding specifies how to interpret the text send by a server.
There is usually no need to change the encoding unless characters are not displayed correctly.

Thank you for your answer.

That dialog window does not select an encoding, it installs a number of encodings which appear already available in the menu. If you can clarify the function of that window, please do.

Which window are you referring to?

Can you attach a screenshot?

• http://en.wikipedia.org/wiki/Screenshot

Use a compressed image type like PNG or JPG to save the screenshot and make sure that you do not exceed the maximum file size (1 MB).

This window. I listed the menu selection to display it in the first post. Thank you for your interest.

I think that you can use that window to make a list of encodings that you use frequently.
That list is accessible via the View > Character Encoding menu without the need to open the sub menus each time.
I don't think that there is more than that.

Yes, but the list in the view menu is longer than the list in the Customize Character Encoding dialog window. Probably they add often used encodings to the permanent encodings selected in the dialog window. Thank you for you answer.

Firefox caches the last used encodings and adds them automatically to the list that you see in View > Character Encoding

You can see that list in the pref intl.charsetmenu.browser.cache on the about:config page.

• http://kb.mozillazine.org/about:config