  We show that if $Y$ is the boundary of an almost-rational plumbing, then the
framed instanton Floer homology $\smash{I^\#(Y)}$ is isomorphic to the Heegaard
Floer homology $\smash{\widehat{\mathit{HF}}(Y; \mathbb{C})}$. This class of
3-manifolds includes all Seifert fibered rational homology spheres with base
orbifold $S^2$ (we establish the isomorphism for the remaining Seifert fibered
rational homology spheres$\unicode{x2014}$with base
$\mathbb{RP}^2$$\unicode{x2014}$directly). Our proof utilizes lattice homology,
and relies on a decomposition theorem for instanton Floer cobordism maps
recently established by Baldwin and Sivek.
