Firefox can be a memory hog, I found this
restart button is quick and painless, when it gets logy just hit the button. Pages you want to keep can be pinned and will reopen no prob. Worth a try...
That's great if One can read this: このアドオンについて カスタムボタンに再起動ボタンを追加します． アドオン開発中などに出しておくと便利です．