I downloaded the latest version of Thunderbird for Windows 10. I installed it. I started it from my non-administrator account. I entered the server information. After a couple of minutes, I realized that I had forgotten to un-check the box to synchronize messages (which can fill gigabytes of my hard disk). I un-checked it. But Thunderbird kept downloading messages. I rebooted, then uninstalled Thunderbird. It kept my account settings. (I wish that the uninstaller would give an option to remove *all* files!) I opened Windows Explorer and did a search from the administrator account to try to remove old files and folders with "Thunderbird" in their name. It found nothing. I switched to my non-administrator account and tried another search. It found two folders named Thunderbird under AppData. I removed them. I rebooted. Then I reinstalled Thunderbird. I was able to be quick enough to un-check the box to synchronize accounts before it downloaded too much data (luckily I have slow Internet, so not too much was downloaded before I could cancel!). I tapped the Alt key to force Thunderbird to show the menu bar. I clicked the View > Toolbars item. It showed a list of toolbars. The "Quick Filter" toolbar was greyed. How do I get the Quick Toolbar option? It works on all of my other Thunderbird installations. Thank you. PS: I suggest adding a setup option to ask whether to synchronize all messages -- to prevent downloading gigabytes of messages that (apparently?) can't easily be deleted. My laptop has a total of 64 GB of storage.