Windows 10 Pro, v1909, desktop. Firefox 73.0.1. Long story, but this is a new installation of Firefox on 2/20. I have 10 extensions installed and sync has been working with no problems with my laptop (same windows and ff versions) since the new installation. Today after my desktop being up for a few hours, sync suddenly failed with an extension-storage error:

Sync.Engine.Extension-Storage ERROR Syncing {d10d0bf8-f5b5-c8b4-a8b2-2b9879e08c5d}: request failed: Error: Response from server unparseable (HTTP 502; SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data): ...
Full Log File Here: error-sync-1582556739519.txt - Google Drive

In the next sync:
1582558258669 Sync.Engine.Extension-Storage ERROR Syncing {d10d0bf8-f5b5-c8b4-a8b2-2b9879e08c5d}: request failed: TypeError: NetworkError when attempting to fetch resource. No traceback available
Full Log File Here: error-sync-1582558258687.txt - Google Drive

And then I get:
1582561417318 Sync.Engine.Extension-Storage ERROR Syncing {d10d0bf8-f5b5-c8b4-a8b2-2b9879e08c5d}: request failed: Error: Timeout while trying to access https://webextensions.settings.servi...WIbxE5kYbqDE7k with {"headers":{"Accept":"application/json","Content-Type":"application/json","Authorization":"**** (suppressed)"},"mode":"cors"}(resource://services-common/kinto-http-client.js:2691:5) JS Stack trace: NetworkTimeoutError@kinto-http-client.js:2691:5
[13]</timedFetch/</_timeoutId<@kinto-http-client.js:2883:18
Full Log File Here: error-sync-1582562018568.txt - Google Drive

From about:support I see that this ID belongs to the Adblock Plus extension.

Then another sync yields:
1582564129295 Sync.Engine.Extension-Storage ERROR Syncing printedit-we@DW-dev: request failed: Error: Timeout while trying to access https://webextensions.settings.servi...zwVYbSsA8LMLm8 with {"headers":{"Accept":"application/json","Content-Type":"application/json","Authorization":"**** (suppressed)"},"mode":"cors"}(resource://services-common/kinto-http-client.js:2691:5) JS Stack trace: NetworkTimeoutError@kinto-http-client.js:2691:5
Full log file not included.

The last two looks like network issues. Network is on with no known problems. VPN is turned off.

Anyone have a clue as to what is going on. I am scratching my head.

- - - Updated - - -

Update: Looks like these sync errors are intermittent. I am getting successful syncs as well. It's been about 3 hours since a sync error. Perhaps this is normal behavior for firefox??