Using browser.storage.sync vs storage.local in Firefox Extensions: When to Use Each

Firefox extensions have two main storage options: browser.storage.sync and browser.storage.local . Picking the wrong one leads to frustrating UX. Here's how to think about it.

The Core Difference

storage.sync storage.local

Synced across devices Yes (via Firefox Sync) No

Quota 100KB (8KB per item) 10MB

Requires Firefox Sync Yes, to actually sync No

Falls back gracefully Yes (local if not synced) N/A

storage.sync: User Preferences

Use sync for anything that should feel the same across all the user's Firefox installations:

// Settings that should follow the user await browser . storage . sync .…