I want to show/hide the bookmark toolbar in Firefox. The only way to do this at the moment is via Alt + V + T + B. Now, that's a lot of buttons to press for something I'd like to do all the time. Is there a way to automate this process by using any sane combination (two buttons)?
As you know there's no shortcut for this like you would have in Chrome or Opera, and as of this writing (early 2018) there are no straightforward ways of customizing Firefox's keyboard shortcuts anymore.
The Hide BookmarksBar extension used to be a pretty okay option, and might still be if you are fine with running one of the ESR releases or a third-party fork of Firefox that still supports "legacy" extensions.
However, as noted in that other SU post, the "Hide BookmarksBar" extension longer works in current mainstream versions of Firefox. Given the present limitations of the WebExtension API, it seems unlikely at the moment that the HideBookmarksBar extension could be updated to work again as a WebExtension.
For these reasons, I would encourage you to voice your support and/or vote for Firefox bug #1328637 ("Personal toolbar lacks a keyboard shortcut to show/hide the bar") on Mozilla's bug tracker.