Support for Private Browsing (a.k.a. Incognito Mode)
Currently, when using deviantART Filter in a private browsing session, the settings and filtered users are NOT loaded. Additionally, when filtering a user (or making any other setting change), those changes only persist until the private window is closed.
This seems to be intentional browser functionality.
Using a different storage mechanism (like storage.local) may allow data to be shared between regular and private browsing modes; however, implementing this may be a breach of users' privacy.
Maybe the settings should be shared between modes, and (if possible) a new setting introduced that would allow the user to choose if their filters are shared between regular and private modes (or not).
This one is probably going to slip to version 5.1 (or later), as it is new functionality that is both complex and not highly requested (as of now, at least).
I enabled allowing the extension in private windows in Firefox and it works just fine and keeps my settings.