@Margybud
Try this...
On the address bar type: about:config ( and click enter )
And it'll appear this warning: Accept all risk ( or something like that ) (Click on it)

And then, go find these...

_ lightweightthemes.persisted.footerURL ( double click and it changes to 'false' )
_ lightweightthemes.persisted.headerURL ( double click and it changes to 'false' )
_ Close the browser. Re-open it and done.