Fire Drake vs Martian Orange

How close are they?

ΔE 20.3, loose: different enough that you should pick on purpose. Martian Orange is a little darker, much more saturated, cooler than Fire Drake.

Can I use Martian Orange instead of Fire Drake?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Martian Orange is a little darker, much more saturated, cooler than Fire Drake.

Can I use Fire Drake instead of Martian Orange?

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

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.