Thunderbird doesn't really care much which version of Windows you're using. Just download the appropriate version from the Lightning page.

https://addons.mozilla.org/en-US/thunderbird/addon/lightning/versions/

I tried your link on my W7 laptop to no avail. There were numerous options to select from, but none appeared to apply to Mozilla Calendar.

Did you not understand that the calendar function is called Lightning? If not, then what are you looking for?

Zenos said

Did you not understand that the calendar function is called Lightning? If not, then what are you looking for?

I'm confused: My Windows XP computer has the calendar I use listed as "C:\Program Files\Mozilla Thunderbird\thunderbird.exe" & also says I'm using version 31.2.0

Given that you're using TB 31.2.0, I think this is the version of Lightning that you need:

https://addons.mozilla.org/en-US/thunderbird/addon/lightning/versions/3.3

Had you specifically and deliberately chosen to stay with an old version of Thunderbird? If you choose to stay with a particular version and refuse updates, then you do also cut yourself off from the mainstream, and offers of help won't be immediately relevant, since addons will assume you're on the current version of Thunderbird.

So now, for example, rather than doing the easy obvious procedure to install an addon, you have to find and download then manually install the Lightning addon.

The following talks about how to install addons.

http://xenos-email-notes.simplesite.com/416814616

But I'll say again; your version of Windows is not relevant when choosing a Lightning download. What you do need to match is the version of Thunderbird that you're using.

Zenos said

Given that you're using TB 31.2.0, I think this is the version of Lightning that you need: https://addons.mozilla.org/en-US/thunderbird/addon/lightning/versions/3.3 Had you specifically and deliberately chosen to stay with an old version of Thunderbird? If you choose to stay with a particular version and refuse updates, then you do also cut yourself off from the mainstream, and offers of help won't be immediately relevant, since addons will assume you're on the current version of Thunderbird. So now, for example, rather than doing the easy obvious procedure to install an addon, you have to find and download then manually install the Lightning addon. The following talks about how to install addons. http://xenos-email-notes.simplesite.com/416814616 But I'll say again; your version of Windows is not relevant when choosing a Lightning download. What you do need to match is the version of Thunderbird that you're using.

Thanks very much. However, my goal is to download new Calendars to my W7 laptop & W8.1 All in One PC (which I intend to convert to W10). The W7 C Calendar can be independent but I may (it's not necessary) like to sync the W8.1 PC with my WXP PC. Does this change your response?

Not really. Lightning is a component of the Thunderbird email program and doesn't really or usefully connect with the calendar function that may be offered within Windows.

If you wish to synchronise multiple computers and have them share a calendar, then Lightning is a possibility. It can synchronise with online calendars using ics, wcap and caldav. Personally I use Google Calendar and caldav, but any online calendar that uses any of those protocols could also be used.

Zenos said

Not really. Lightning is a component of the Thunderbird email program and doesn't really or usefully connect with the calendar function that may be offered within Windows. If you wish to synchronise multiple computers and have them share a calendar, then Lightning is a possibility. It can synchronise with online calendars using ics, wcap and caldav. Personally I use Google Calendar and caldav, but any online calendar that uses any of those protocols could also be used.

Thanks very much for you help (some of which is over my 73 year old head). My only goal is to keep things simple & use Windows for accessing my Comcast home page for emails & find a useful free calendar I can use to get reminders (up to a week before or day or two before) of upcoming events & appointments. What are some calendar suggestions that would suit my needs?

I promise I won't bug you anymore!