After last upgrade of ThunderBird there is no arrows on the end of scrolling bars to scroll line-by line. I am not sure what was the earlier ThunderBird version, but now I have 52.3.0. The problem is same in 32 bit Ubuntu Xenial and 64 bit Debian Stretch. All scrolling bars seem to be affected: e-mail list, email view pane, accounts pane. I have to use arrow keys or mouse wheel. PS Same problem is with Mozilla Firefox. It might be the design feature, but I myself prefer when programs behave alike on my desktop. All other programs have scrolling bars with arrows on the ends.