Created attachment 8659837 [details] Thunderbird changing size and apparent resolution while freezing temporarily under Windows 10.png User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:40.0) Gecko/20100101 Firefox/40.0 Build ID: 20150826023504 Steps to reproduce: While migrating through different folder, e.g. from in to Sent box have random 'freezes' and changes in Thunderbird apparent screen/resolution size. This began after I updated to Win 10. Actual results: For about 10 seconds Thunderbird stops responding while the screen has reduced in size from full screen to partial and the apparent resolution has changed. I took a screen print with Thunderbird 'not responding'. Note that it was in full screen mode and has reduced in size and moved to the upper right of the screen. Expected results: Folder should have opened without the window or resolution size changing.
Start *Windows'* safe mode with networking enabled - win10 http://windows.microsoft.com/en-us/windows-10/change-startup-settings-in-windows-10 Still In Windows safe mode, start thunderbird in safe mode - http://support.mozillamessaging.com/en-US/kb/safe-mode Does problem go away?
If you still see this when using a current version please offer more information.