Firefox sync never works after waking up computer from sleep mode. I always use my computer with sleep-mode, I rarely shut-down my computer. So I never terminate my Firefox sessions or close it completely. After waking up computer from sleep mode, You are expected to continue working from where you left off. So you continue to sync your bookmarks and so on. But Firefox Sync never synchronizes your bookmarks or data in the situation after waking up computer from sleep mode. It is a big problem. I think Firefox sync service can not handle or recognise the computer sleep-mode.