Credit to user Scorpio for this info found on another review:

If the lightning animation stops and you want it to continue running:
1) Open a new tab and enter "about:config" in the URL bar
2) Search for "lightweightthemes"
3) Double-click "lightweightThemes.persisted.footerURL" and "lightweightThemes.persisted.headerURL" to change their values from true to false
4) Restart Firefox