Hi. I currently have a very bad problem with my Firefox sync. I have a few devices. 1. My primary desktop, running Windows 10 Enterprise 1607 x64bit ===> This one has a very "aged" Firefox profile dating back many, many years since I have used the browser for the first time. Running Firefox V55 latest (EN-US, x86). 2. My gaming laptop, only rarely used. Running Windows 10 Enterprise 1607 x64bit and Firefox V55 latest (EN-US, x86). 3. My small laptop, very recently acquired. Software configuration is same as above. + Some of the addons used are the "Legacy" type Story goes like this. - The desktop was working properly. I sync my data using the FF sync account that has my email [lets say this is my email X] and registers correctly. I click the refresh button to "sync" the data and it spins blue, indicating that the data sync in progress, then stops to indicate the data sync is finished. - I acquired my gaming laptop, I installed a fresh version of FF and logged in using my FF sync account. I waited a while since I had lots of bookmark and history in addition to a plethora of addons. After not too long, the FF copy on my gaming laptop has the same bookmark/history/addon as my desktop one. The sync works perfectly with the gaming laptop and desktop version of FF. - The gaming laptop goes into hiatus of usage and a few addons were changed / swapped around on the main desktop. I then acquired this small laptop. - I installed FF on the small laptop and proceeded to login with my FF sync account. However I noticed that FF was taking quite a lot of the dual core ULV cpu, around 30-45%. I thought of this as normal since my FF sync account carries a large bulk of my desktop data. =Problem start to appear here= - For some reason, after 10-15min being left alone, the small laptop's sync procedure haven't finished. I was concerned of this because of the lack off addons synced (but there are bookmarks and history). I proceed to close down FF on the small laptop, planning to let sync work again. Surprisingly, FF didn't close when I click the X or power button by (accessed by the three stripes on top right). - I tried to verify this on my gaming laptop, to see if sync would "clone" my desktop's addons setting to the laptop. Surprisingly the same problem occurs on both the laptop and desktop! Now all machine are suffering from the infinite sync progress issue. ++Additionally++ - After browsing a while, doing random actions such as accessing taskbar bookmark will crash or even loading a page will crash the browser into a non-operative state. =Now I have to troubleshoot the machine(s)= - I tried with the small laptop to completely clean uninstall FF by using Revo uninstaller + manually sweeping the appdata. This solution didn't work and even with a fresh .exe installer (offline) the same problem continues - "Refresh" FF on the desktop (and update add-ons if possible to webtext version) then I delete my sync account that is tied to email X, then creating a new sync account using the same email X on my desktop. This made the sync "work" in a sense that the progress icon stopped spinning. But the two laptops still exhibited the infinite sync progress icon problem. - AFTER the attempt made above, exiting FF (followed by the bug of: FF process not shutting down when closed) on either laptops will either corrupt/messup the FF profile forcing me to delete them and "start fresh" - Restarting computers - Running AV scans (clean) - Restarting modem None of the laptops nor my main desktop have experienced this problem before and I am confused! Does anyone have a solution to the problem above? I included the system information from my main desktop on this post. I can submit more with the gaming/small laptop if need be. Thanks in advance.