better as subfolder of Unsorted Bookmarks ("system") folder Rated 5 out of 5 stars

In Fox 3.5.x library, ctrl+shift+b, see Unsorted Bookmarks

Tark might be better served creating two subfolders in Unsorted Bookmarks (each at the same depth with respect to Unsorted Bookmarks)

"Might be of interest"
"I guess I have forgotten about these"

Or something comical.

Retain the "bookmark expiration" nature of tark. Consider adding your tark-icon next to the "bookmark this page" star in the location bar much like Read It Later does. Make that button either click sequentially- or click and hold to change tark state.

Similarly tark will change the color- or shape of this new location bar button itself instead of modifying the favicon (which I disable entirely but that is not the reason for not wanting to use favicon).