Open the page in SharePoint Designer 2013 and comment out the script where you close the tab.
If SharePoint Designer isn't allowed in your organisation, download the page from the pages library and edit in Notepad or any other text editor. When your done, upload the page to the pages library again.
And for usability, closing a tab when browsing to it is really bad. It does not only confuse your users; they may think SharePoint is down or their computer malfunctioning. So please, don't implement such a solution.