There was one extension I used in Chrome that I haven't found a Firefox replacement for, but I stopped trying to look a while ago and just live without it.
Was a specific kind of cookie manager: you could whitelist a set of websites to keep their cookies. Everything else would be deleted when you told the extension to do so.
Too many websites need cookies that stick around indefinitely. But I also don't want to delete everything everytime I close Firefox, because I may want to keep a website around for a few days without wanting to bother adding it to a whitelist.
I want something more complex than a basic whitelist and blacklist. I already use that in Firefox and it helps somewhat but not wholly. I want to manage specifically when it happens and in accordance to said lists. I haven't found anything that handles that in the settings.