That is really strange, because it sounds like "b" is calling Duplicate Tab on your Firefox (and the letter b doesn't even appear in that phrase). Do you use any extensions that may allow customizing keyboard shortcuts? You can view, disable, and often manage or remove extensions on the Add-ons page. Either: * Ctrl+Shift+a (Mac: Command+Shift+a) * "3-bar" menu button (or Tools menu) > Add-ons * type or paste '''about:addons''' in the address bar and press Enter/Return In the left column of the Add-ons page, click Extensions. On the right side, find the "Manage Your Extensions" heading. Then scan down that list -- anything relating to keys or tabs that might be creating this shortcut? ''You can ignore anything below the "Recommended Extensions" heading.'' ---- By the way, Firefox 70 is no longer supported. Is that the latest for your build of Ubuntu? You could consider switching to a Mozilla build of Firefox instead.