I don't know what the full size is, but it is a lot since I'm trying to move my entire Mendeley library here. Nothing has yet been synced, though- my web account and app seem to have completely different items.
I deleted everything in my library, and the sync still seems to hang. I did get it to sync once when I first installed the software, but it won't work anymore.
Yeah, let's try starting over. Find your Zotero data directory, close Zotero (or Firefox if you're using Zotero for Firefox), and delete the data directory. Then start Zotero again and you should have an empty library. What happens when you then try to sync, exactly?
When I click "Submit to Zotero Server" I get the error message, "Invalid response from server."
So, here are the first few lines of the output of that log (the complete log is too long to post):
[JavaScript Error: "incoming.telemetry.mozilla.org:443 uses an invalid security certificate.
The certificate is not trusted because the issuer certificate is unknown.
The server might not be sending the appropriate intermediate certificates.
An additional root certificate may need to be imported.
(Error code: sec_error_unknown_issuer)
"]
[JavaScript Error: "1457650961466 Toolkit.Telemetry ERROR TelemetrySend::_doPing - error making request to https://incoming.telemetry.mozilla.org/submit/telemetry/e8e3be81-4242-d94b-9e67-02eba04c0a56/main/Zotero/4.0.28.8/release/20151003?v=4: error" {file: "resource://gre/modules/Log.jsm" line: 749}]
If this is a work machine, your IT department may be intercepting your connection. If not, it's likely due to the HTTPS scanning feature of security software that you're running.
Upgrade Storage
So, here are the first few lines of the output of that log (the complete log is too long to post):
[JavaScript Error: "incoming.telemetry.mozilla.org:443 uses an invalid security certificate.
The certificate is not trusted because the issuer certificate is unknown.
The server might not be sending the appropriate intermediate certificates.
An additional root certificate may need to be imported.
(Error code: sec_error_unknown_issuer)
"]
[JavaScript Error: "1457650961466 Toolkit.Telemetry ERROR TelemetrySend::_doPing - error making request to https://incoming.telemetry.mozilla.org/submit/telemetry/e8e3be81-4242-d94b-9e67-02eba04c0a56/main/Zotero/4.0.28.8/release/20151003?v=4: error" {file: "resource://gre/modules/Log.jsm" line: 749}]
[JavaScript Error: "1457650961466 Toolkit.Telemetry ERROR TelemetrySend::sendPersistedPings - failed to send ping e8e3be81-4242-d94b-9e67-02eba04c0a56: {"isTrusted":true}" {file: "resource://gre/modules/Log.jsm" line: 749}]
If this is a work machine, your IT department may be intercepting your connection. If not, it's likely due to the HTTPS scanning feature of security software that you're running.