Could you check whether you have dual homepages?

orange Firefox button or classic Tools menu > Options > General

If you see more than one URL in the Home Page box, delete the extra one and the vertical bar that separates them.

More info: How to set the home page | How to | Firefox Help.

Any luck?

Edit: if the page appears in the sidebar, which also can be used to display bookmarks (Ctrl+b) or history (Ctrl+h), then it probably is caused by something other than your home page setting.

Thanks for the quick reply. Unfortunately, only one homepage is listed. Problem still there.

Could you post a screen shot? I'm having a little trouble picturing the relationship between the two pages.

Also, do you recall installing any toolbars or other add-ons from Sam's club that could be popping up an extra window?

Please see attached for screenshot. Thanks.

Hmmm, it looks as though there is a small X to close that sidebar in the dark area above the Sam's Club logo. I'm still not sure why that page opened there in the first place. One possibility is that you added a bookmark from the site. Sites often set an option to open their pages in the sidebar. You can change that by editing the bookmark properties (uncheck the box toward the bottom of the Properties dialog).

jscher2000 -- you are a genius! I closed it and it does not reappear now when I open Firefox. I checked the properties of the Sam's Club bookmark I had set, and the box "open in sidebar" was not checked -- but maybe it was at one point. Anyway, seems to have fixed the problem. Many thanks. This was an annoyance that I could not find answers too on any other website. you did it!