In Firefox 3.6 ImgLikeOpera does what I want: I can selectively download images I want to view, have some sites that show images by default, show only cached images etc. The only issue is slight incompatibility with AutoPager.
Hovewer, in Firefox 4 I don't see any flexible image visibility manager: ImgLikeOpera 0.6.20 works bad (Ctrl+Rightclick fails, Alt+M fails, no toolbar item etc.) and ImageBlock 2.1 is too simple - I don't see image placeholders and can't show them individually?
Are there some another extensions that I should try?