Post date: Feb 17, 2018 10:04:17 AM
Try this please, it might help!
Open a new tab, and type “about:config” at the URL bar, then search for “lightweightthemes” with the filter.
Change the values of “lightweightThemes.persisted.footerURL” and “lightweightThemes.persisted.headerURL” from true to false( by double click on them).
After doing so, restart Firefox and you will see it works! You don’t have to install any add-on.
I do hope it helps!! And the source I got this from is from this forum: https://support.mozilla.org/en-US/questions/965834