Fire Drake vs Ogre Brown

How close are they?

ΔE 21.5, loose: different enough that you should pick on purpose. Ogre Brown is a little lighter, more saturated than Fire Drake.

Can I use Ogre Brown instead of Fire Drake?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Ogre Brown is a little lighter, more saturated than Fire Drake.

Can I use Fire Drake instead of Ogre Brown?

The same difference applies the other way round: Fire Drake is a little darker, more muted.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.