tl;dr: Use gifsicle to minify GIFs.

brew install gifsicle

wget https://upload.wikimedia.org/wikipedia/commons/c/c8/132C_trans.gif

gifsicle 132C_trans.gif -O3 -o 132C_trans.min.gif

2.2M 132C_trans.gif
1.7M 132C_trans.min.gif

The gifsicle tool was able to optimize the file by (2.2 - 1.7) / 2.2 * 100 = 23%; this is a material improvement.