Here have the end of my weave log (the begining exactly looks like yourse).. By the way, the JSON exception does not look good:
Idle timer created for sync, will sync after 1 seconds of inactivity.
GET success 200 http://DOMAIN/PATH/ld2/firefox-sync/1.0/USER/info/collections?v=1.3
Exception: JSON.parse JS Stack trace: ()@resource.js:261 < ()@util.js:317 < ()@service.js:1214 < WrappedNotify()@util.js:114 < WrappedLock()@util.js:86 < WrappedCatch()@util.js:65 < sync(false)@service.js:1166 < ([object Object])@service.js:440 < notify([object XPCWrappedNative_NoHelper])@util.js:629