Dear All, The Subject pretty says it all: when I start Thunderbird, windows show the elevators at the right side as they are supposed to. However a few seconds later the elevators disappear and do not show up when moving the mouse pointer over the right side as they used to. The only way around this I found so far is to click on the arrow keys and quickly move the mouse pointer to the elevators handle for click and dragg in order to scroll up and down the window. This problem happens in all Thunderbird's interface windows: accounts and folders window, mailbox message list and message content. This issue only started after installing the latest 91.3.0 (64bit) Thunderbird version. I am using a MacBook Pro, running OS X 14.6 (Mojave). Any help will be appreciated, it is quite annoying Best regards, -- joão