First of all your Flash plugin is out of date: Use Adobe's own page to test your version of the plug-in and to update it www.adobe.com/software/flash/about/ -- evidently the same information is not getting to the Mozilla plug-ins test. That might fix your problem if your home page uses Flash such as a news site. Find updates for installed plugins at www.mozilla.com/plugincheck/mozilla.com/plugincheck plugin page keeps coming up: see https://support.mozilla.com/en-US/questions/832793 particularly the replies near the end (different replies for different users).

* whenever I open the browser, the check plugins page always opens in a second tab.  How can I make this stop?

Expect problem seen here has been fixed, see Cor-el's reply to question 833760 in * [https://support.mozilla.com/questions/833760 whenever I open the browser, the check plugins page always opens in a second tab. How can I make this stop?]