Similar to this issue https://support.mozilla.org/en-US/questions/796251 , can't sync the content of my browser while behind a company proxy. My configuration: Firefox 26.0 - Win 7 Extract of a report when accessing "about:sync-log" : 1389967592393 Sync.Service INFO Loading Weave 1.28.0 1389967592395 Sync.Engine.Clients DEBUG Engine initialized 1389967592398 Sync.Engine.Clients DEBUG Resetting clients last sync time 1389967592406 Sync.Tracker.Bookmarks WARN Changed IDs file bookmarks contains non-object value. 1389967592406 Sync.Engine.Bookmarks DEBUG Engine initialized 1389967592409 Sync.Tracker.Forms WARN Changed IDs file forms contains non-object value. 1389967592409 Sync.Engine.Forms DEBUG Engine initialized 1389967592411 Sync.Tracker.History WARN Changed IDs file history contains non-object value. 1389967592411 Sync.Engine.History DEBUG Engine initialized 1389967592413 Sync.Tracker.Passwords WARN Changed IDs file passwords contains non-object value. 1389967592413 Sync.Engine.Passwords DEBUG Engine initialized 1389967592415 Sync.Engine.Prefs DEBUG Engine initialized 1389967592417 Sync.Engine.Tabs DEBUG Engine initialized 1389967592418 Sync.Engine.Tabs DEBUG Resetting tabs last sync time 1389967592421 Sync.Tracker.Addons WARN Changed IDs file addons contains non-object value. 1389967592421 Sync.Engine.Addons DEBUG Engine initialized 1389967592422 Sync.Service INFO Mozilla/5.0 (Windows NT 6.1; WOW64; rv:26.0) Gecko/20100101 Firefox/26.0 1389967592423 Sync.SyncScheduler DEBUG Clearing sync triggers and the global score. 1389967592424 Sync.Status DEBUG Status.service: success.status_ok => success.status_ok 1389967592424 Sync.Service DEBUG Caching URLs under storage user base: https://xxxx.xxxxxxxx.xxx/remote.php/mozilla_sync/1.1/xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ 1389967592424 Sync.Status DEBUG Status.service: success.status_ok => success.status_ok 1389967592424 Sync.AddonsReconciler INFO Registering as Add-on Manager listener. 1389967592424 Sync.AddonsReconciler DEBUG Adding change listener. 1389967592426 Sync.Status DEBUG Status.service: success.status_ok => success.status_ok 1389967592427 Sync.Tracker.AdblockPlus WARN Changed IDs file adblockplus contains non-object value. 1389967592427 Sync.Tracker.AdblockPlus.private WARN Changed IDs file adblockplus.private contains non-object value. 1389967592427 Sync.Engine.AdblockPlus DEBUG Engine initialized 1389967592428 Sync.Status DEBUG Status.service: success.status_ok => success.status_ok 1389967593513 Sync.Status DEBUG Status.service: success.status_ok => success.status_ok 1389967596428 Sync.Status DEBUG Status.service: success.status_ok => success.status_ok 1389967596429 Sync.Service DEBUG User-Agent: Firefox/26.0 FxSync/1.28.0.20131205075310. 1389967596429 Sync.Service INFO Starting sync at 2014-01-17 15:06:36 1389967596429 Sync.Service DEBUG In sync: should login. 1389967596429 Sync.Status DEBUG Status.service: success.status_ok => success.status_ok 1389967596429 Sync.Status DEBUG Status.service: success.status_ok => success.status_ok 1389967596429 Sync.Service INFO Logging in user xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 1389967596429 Sync.Service DEBUG Caching URLs under storage user base: https://xxxx.xxxxxxxx.xxx/remote.php/mozilla_sync/1.1/xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ 1389967596579 Sync.Service DEBUG verifyLogin failed: NS_ERROR_PROXY_CONNECTION_REFUSED JS Stack trace: Res_get@resource.js:413 < verifyLogin@service.js:683 < onNotify@service.js:926 < WrappedNotify@util.js:142 < WrappedLock@util.js:97 < WrappedCatch@util.js:71 < login@service.js:937 < @service.js:1174 < WrappedCatch@util.js:71 < sync@service.js:1170 1389967596579 Sync.Status DEBUG Status.login: success.login => error.login.reason.network 1389967596579 Sync.Status DEBUG Status.service: success.status_ok => error.login.failed 1389967596579 Sync.Status DEBUG Status.login: error.login.reason.network => error.login.reason.network 1389967596579 Sync.Status DEBUG Status.service: error.login.failed => error.login.failed 1389967596579 Sync.SyncScheduler DEBUG Clearing sync triggers and the global score. 1389967596579 Sync.SyncScheduler DEBUG Next sync in 86400000 ms. Specially look at the following line: 1389967596579 Sync.Service DEBUG verifyLogin failed: NS_ERROR_PROXY_CONNECTION_REFUSED JS Stack trace: Res_get@resource.js:413 < verifyLogin@service.js:683 < onNotify@service.js:926 < WrappedNotify@util.js:142 < WrappedLock@util.js:97 < WrappedCatch@util.js:71 < login@service.js:937 < @service.js:1174 < WrappedCatch@util.js:71 < sync@service.js:1170 Thanks a lot for your help, Best regards, Alexandre 8)