Firefox has awful performance on nearly any web page for me (2014 Mac). Even its own settings page alone puts a core at 100%. I can get past bad font rendering

Firefox has awful performance on nearly any web page for me (2014 Mac). Even its own settings page alone puts a core at 100%. I can get past bad font rendering and giving up pinch-to-zoom and not reading PDFs in the browser, but I can't give Firefox half my battery life. I'll use it on my work PC but it's still a huge waste of electricity.