Alt+D overrides native browser keyboard shortcut

Alt+D shortcut introduced in #843 prevents its standard behavior: [Select Location Bar](https://support.mozilla.org/en-US/kb/keyboard-shortcuts-perform-firefox-tasks-quickly#w_miscellaneous
) in Firefox / [Jump to the address bar](https://support.google.com/chrome/answer/157179?hl=en) in Google Chrome, which apparently [originates from Internet Explorer](https://blogs.msdn.microsoft.com/oldnewthing/20170314-00/?p=95727).

Creating issue to keep track; personally I'd like to have this removed or remapped to say alt+shift+d or made optional. [Workarounds exists](https://github.com/freeCodeCamp/devdocs/issues/843#issuecomment-428159454).