'October 2013 Update For Root Certificate for Windows XP ' KB 931125 Installed

All of what you mentioned makes good sense and thanks for the links.

When a computer is shut down and turned off but the cable modem is left on, is the computer still connected to the Internet?

If yes and someone continues to use XP after the support end date, should they unplug their modem after shutting off and turning off the computer?

All of what you mentioned makes good sense and thanks for the links.

When a computer is shut down and turned off but the cable modem is left on, is the computer still connected to the Internet?

If yes and someone continues to use XP after the support end date, should they unplug their modem after shutting off and turning off the computer?

The computer isn't connected to the Internet anymore, no. But it's advisable to disconnect it completely by either switching off the power supply if there's a switch available on the back of it, or to remove the power cord. By doing that, you'll be performing a so called 'cold boot' every time you power on. See here for more details: http://www.reference.com/motif/society/difference-between-cold-boot-and-warm-boot

One other thing since you're using Firefox. If you have the view with the orange, oblong Firefox button top left, hit ALT to toggle the text links on and then go to Tools | Options | Privacy,

Next, checkmark the option to "Clear history when Firefox closes" and then click the "Settings" button. In the submenu which appears, checkmark "Cache", but remove the checkmark from the others. Here's a couple of screenshots.

There's malware around which downloads to the browser cache and then sits there waiting for the moment when you inadvertently land on a compromised site and then activates. By clearing the cache every time you close Firefox, anything in there will be deleted automatically.

Is it only necessary to remove the power cord from the back of the modem to turn it off or should the ethernet cable (that connects to the back of the cable modem) and the cable that connects to the cable modem (the other end connects to the wall) be disconnected too?

I am using Firefox 28 and the top left corner shows an orange and blue globe icon. When Alt is pressed, it only highlights the word 'File' that is displayed on the top of the screen-Does this version allows the text links to be 'toggled?'

In the 1st screenshot, should the 'Remember search and form history' and 'Accept cookies from sites' be checked or unchecked?

In the 2nd screenshot, should 'Browsing and download history' and active logins,' and 'Form and search history' options be checked or unchecked?

Is it only necessary to remove the power cord from the back of the modem to turn it off or should the ethernet cable (that connects to the back of the cable modem) and the cable that connects to the cable modem (the other end connects to the wall) be disconnected too?

I am using Firefox 28 and the top left corner shows an orange and blue globe icon. When Alt is pressed, it only highlights the word 'File' that is displayed on the top of the screen-Does this version allows the text links to be 'toggled?'

In the 1st screenshot, should the 'Remember search and form history' and 'Accept cookies from sites' be checked or unchecked?

In the 2nd screenshot, should 'Browsing and download history' and active logins,' and 'Form and search history' options be checked or unchecked?

Remove the power cord from the PC, not the modem. You can leave that running.

As regards "Remember search and form history", that's up to you. See here for more info on what those settings do: Firefox Privacy panel

Same goes for the submenu: Remove recent browsing, search and download history

My own settings are those you see in the screenshots.As regards Cookies, I have that unchecked  because I use this Cookie Manager

I will be clearer in what I am asking:

There is a black wire that connects from the back of the cable modem to the computer power supply and then the wire connects and is plugged into the power bar.

There is a white cable that connects the back of the cable modem and the wall outlet.

There is a grey cable with a jack on each end that connects the back of the cable modem to the Ethernet port at the back of the computer.

What part(s) of each wire/cable should be unplugged once the computer is turned off?

I do not use Cookie Manager or any equivalent-Should that option be checked or unchecked?