Great addon !
It just lacks the ability to set a custom DNS resolver, and the TLSA support.

Besides, the UI doesn't integrate well with a dark theme on Linux (KDE here, but I suspect it will be the same for another window manager), as the background of the tooltip gets its color from the system, and the font color seems to be hardcoded in black.

Oh, and I didn't find any link to the sourcecode. Is it available ? :)