v3.0.4 New Firefox feature and fixes

• ADDED: "Remove navigation bar" toggle in Options. When a Firefox-family browser is selected (Release, Beta, Developer Edition, Nightly, ESR), enabling this option applies a minimal app-like UI via userChrome.css. Back, Forward, Reload, and the app menu remain available, while the tab bar, address bar, bookmarks toolbar, menu bar, and other toolbar buttons are hidden. Chromium-based browsers are unchanged, as they already use --app mode. Extra rules in the free-form CSS boxes are still applied on top of the minimal base or can be used to replace/customize it. This gives Firefox-based apps a similar look and feel to Chromium's --app mode.
• FIXED: Kiosk Mode no longer sticks as a global default. Installing one app with kiosk enabled previously forced every subsequent installation into kiosk mode. Kiosk is now per-app only: it follows store.json's "kiosk": true setting when present, otherwise it defaults to off (normal window).
• FIXED: Desktop file installation. A regression in AppRun caused the --install command to attempt to install the .desktop file directly. AppRun now handles the .desktop installation correctly, so opening the AppImage automatically installs the desktop entry again.