> When I removed loader-spinner.gif, the placeholder we display while the menu options load, the page stopped crashing. Eureka! It’s the gif! We swapped in a different gif and the page did not crash.

I would love to have the original and the un-crashy gifs mentioned. It's super easy, generally, and even without an extensive knowledge of image formats to get a grasp of what might be going on and then going down some really exciting rabbit-hole of image encoding/decoding issues.

Just take the two gifs and run them (one by one) through ImageMagick or GraphicsMagick to print out the details of what's in them, and look for differences.

Assuming ImageMagick is installed (or GraphicsMagick) installed, something like:

#imagemagick

$ diff <(identify -verbose loader-spinner-CRASHY.gif) <(identify -verbose loader-spinner.gif)

#graphicsmagick

$ diff <(gm identify -verbose loader-spinner-CRASHY.gif) <(gm identify -verbose loader-spinner.gif)

...and rabbit-hole away

EDIT: formatting