Can you be more specific? There are no Zotero sync errors in there. What was the actual message you received?
Also, you're running an alpha version of Firefox, so if want help with a recurring issue, please reproduce it in the latest release version first and provide a Report ID from that.
Yeah, that's because you're using an alpha version of Firefox. If you're running an alpha/beta version of Firefox, you should at least run the Zotero beta, since that's where fixes end up sooner, but we only ever guarantee compatibility with the latest released version of Firefox. That particular issue is fixed in the beta, though, and the fix will be included in 4.0.26, which will be out shortly.
Also, you're running an alpha version of Firefox, so if want help with a recurring issue, please reproduce it in the latest release version first and provide a Report ID from that.
I moved 4 Jpg files from one publication to another before the error started.