When I use whitelist mode, this is not comfortable add new hosts always via going to about:config, searching string and editing manually. Will be good to see "Add to whitelist" button in url string that will add current domain to whitelist. Can you do this feature?
I don't have an answer, I'll keep this open so I can evaluate it later.
BTW, how many entries does your whitelist have?
6 domains at now, but this is low number because adding new domain process is not so quickly :)
Normal mode broke some sites (online consultant http://www.jivosite.ru/ on all sites, all sites with separate auth system in subdomain - system.com, other.system.com, other2.system.com), so I can use only whitelist mode for normal working.
Blacklist mode will help too, but it is not so quickly to understand why some functions not working - because multifox block something, or other cause.