mobile-config-autoconfig.js: Use xdg-desktop-portal file-picker (MR 60)

By using the xdg-desktop-portal file-picker we get a more native file-picker, e.g., on Plasma Mobile

Fixes #16.

README.md

@@ -14,6 +14,7 @@ This does not replace a proper implementation in
 * Moves the UI chrome (address- and tab-bar) to the bottom
 * Enable mobile gestures
 * Show one tab to show the page title and add a tab counter
+* Use the native file-picker through xdg-portals
 * Privacy tweaks:
   * Disable search suggestions
   * Disable Firefox studies
@@ -56,6 +57,9 @@ If you don't like the hiding of https:// in the urlbar, you can get back to
 default behavior by setting `browser.urlbar.trimHttps` to false in
 `about:config`.
 
+If you should have issues with the file picker, you can set
+`widget.use-xdg-desktop-portal.file-picker` to 2 in about:config.
+
 If it cannot be changed in preferences, look in
 `/etc/firefox/policies/policies.json`. You can see the active policies while
 Firefox is running in `about:policies`. The uBlock origin add-on for example,

src/mobile-config-autoconfig.js

@@ -324,6 +324,10 @@ function set_default_prefs() {
     // Hide https:// in urlbar by default to save space and make more relevant
     // parts of the urlbar visible.
     defaultPref('browser.urlbar.trimHttps', true);
+
+    // Use the xdg-desktop-portal.file-picker by default, e.g., for a native
+    // file-picker instead of gtk-file-picker on Plasma Mobile
+    defaultPref('widget.use-xdg-desktop-portal.file-picker', 1);
 }
 
 function main() {