Well, this is a fascinating development, first letter navigation works in the Chrome Bookmarks list whether you have a screen reader active or not, and it works just like when a screen reader is active (without narration, of course).
If I hit Enter once sitting on a Bookmark I want to open it opens in the tab I'm currently in. So if you know you want a page to open in a tab of its own open that tab with CTRL+T first, then follow that by ALT + Down Arrow, B then start with first letter nav.
Brian - Windows 10 Home, 64-Bit, Version 1803, Build 17134
A great deal of intelligence can be invested in ignorance when the need for illusion is deep.
~ Saul Bellow, To Jerusalem and Back