I'm not sure.

Try refreshing FF.

Because of this strange issue, I recently completely reinstalled Xubuntu and Firefox. Sorry, if I had to reinstall/refresh FF all the time, I'd rather stop using my favourite browser.

BTW: It also happens on my Win8.1 PC an FF 74.0.

THIS SHOWS, THAT IT IS A BUG, NOT MY FAILURE OR CONFIG.

This issue has been reported before for the German Firefox version. In the German version Alt+D is reserved for the File menu (Datei) and thus isn't available for focusing the location bar.

• /questions/1230509 Alt + D showing menu instead of fucusing search bar
• Bug 1485052 - Alt + D opens the file menu for german users instead of focusing the search bar

(please do not comment in bug reports
https://bugzilla.mozilla.org/page.cgi?id=etiquette.html)

You can possibly use Firefox in a locale other than DE if you want to use Alt+D for the location bar.

• https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

I realize this doesn't change the shortcut back, but does it work to separate those: tap Alt to activate the menu bar, then tap D ?

Sorry I appear to have misread your question.

I installed the DE language pack and can confirm the changed behavior.

It still shows "s" as access key for the urlbar access key in browser.dtd.

• view-source:chrome://browser/locale/browser.dtd
• https://dxr.mozilla.org/l10n-mozilla-release/source/de/browser/chrome/browser/browser.dtd

Maybe this is related to switching to fluent and some access keys can no longer be overridden by a localization.

To make the Alt key work to show the menu bar, you need to have this pref set to true on the about:config page.

• ui.key.menuAccessKeyFocuses = true