The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. Note: This will cause you to lose any Extensions, Open websites, and some Preferences.

To Reset Firefox do the following:

1. Go to Firefox > Help > Troubleshooting Information.
2. Click the "Reset Firefox" button.
3. Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
4. Firefox will open with all factory defaults applied.

Further information can be found in the Refresh Firefox - reset add-ons and settings article.

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Thank you for the information. I have already fixed the problem. The information you provided will help me with other issues though. Again thanks!

Opening in the sidebar is the default for bookmarks that are created via a link or button on a website.
You can check the Properties of a bookmark via the right-click context menu in the sidebar (Ctrl+B; Cmd+B on Mac).
In the Bookmarks Manager (Bookmarks > Show All Bookmarks) you can click the More button in the Details pane at the bottom right.
Make sure that "Load this bookmark in the sidebar" is not selected.

Thank you for this information. I found out how to close the page after I posted the question. The information that you provided is helping me with other problems I am having. Again thanks for your time in answering my question.

Thank you.