Many users like me set Firefox preferences in such a way that every time someone close Firefox, Cookies & Sites Preferences get cleared.
Hence, to load my customized setting, either I have to enter Pass-phrase. This problem can be solved by storing Duckduckgo site preferences like theme, WOT on/off, Search results font and Privacy settings etc. inside Duckduckgo add-on, so that user don't have to set them every time. Also option for reset settings to default can be provided in case required.
If there is any problem in implementing this and serving User Privacy Goals simultaneously then my settings should be loaded automatically everytime I open DDG website in a similar way Firefox fills saved password. The pass-phrase for DDG cloud settings can be stored in an encrypted for within Firefox or within DDG Plus Add-On.
Please comment/reply/discuss this.. That will help me to understand other aspects or problem in implementing this..