User Agent: Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/47.0.2526.106 Safari/537.36 Steps to reproduce: Update from 43 to 43.0.2 Actual results: After last update Firefox lost the hability to connect to any site or sync account information. Expected results: Show sites and sync account info. Reinstalling the 43 version works as expected again.

Any info shown?

None at all. If you put an address or a search string, the tab text flashes (very fast) with "Loading" text and then restores the previous "New tab" text, but nothing happens, nothing changes, no error, nothing. The same for the Sync action, flashes the sync icon to blue and back to black. If I disconnect the account and then try to setup again with "Connect" button, the "No connection" tab with "Try again" shows up. Labels may not be exact, I'm using the spanish version. I can confirm that version 43.0.1 works, so something happens with 43.0.2.

See the https://bugzilla.mozilla.org/show_bug.cgi?id=1233237#c17 and https://bugzilla.mozilla.org/show_bug.cgi?id=1233237#c32.

you could try uninstaling the nvidia forceware network access manager from your system control panel: https://support.mozilla.org/en-US/kb/connectivity-crashing-firefox-43-update/