Are firefox bugs cross platform?

I use Ubuntu and last firefox version.

I opened an image with firefox, and a crash occurred.

Let's assume it's a crafted jpg to run an exploit, and execute arbitrary code.

To sum up: (1) Firefox opens a crafted JPG ->(2) Firefox crashes ->(3) Arbitrary code try to run

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Step 3: According to Are exploits platform dependent?, exploits are platform dependent.

My question is about step 2: A bug is the origin of the crash. The crafted jpg uses this bug.

Can crash occurs on every platform ? If yes, so it will be harmful only for one OS ?

Thank you