diff --git a/apps/geolibre-desktop/src/components/layout/toolbar/ProjectFileDialogs.tsx b/apps/geolibre-desktop/src/components/layout/toolbar/ProjectFileDialogs.tsx
index bf83532ae..e7569f4a0 100644
--- a/apps/geolibre-desktop/src/components/layout/toolbar/ProjectFileDialogs.tsx
+++ b/apps/geolibre-desktop/src/components/layout/toolbar/ProjectFileDialogs.tsx
@@ -15,7 +15,7 @@ interface ProjectFileDialogsProps {
   projectFiles: ReturnType<typeof useProjectFileActions>;
 }
 
-/** The project-file dialogs: Open-from-URL, the error dialog, and the env-var strip prompt. */
+/** The project-file dialogs: Open-from-URL, the error dialog, the save-name prompt, and the env-var strip prompt. */
 export function ProjectFileDialogs({ projectFiles }: ProjectFileDialogsProps) {
   const { t } = useTranslation();
 
@@ -85,6 +85,55 @@ export function ProjectFileDialogs({ projectFiles }: ProjectFileDialogsProps) {
           </div>
         </DialogContent>
       </Dialog>
+      <Dialog
+        open={projectFiles.saveNamePrompt !== null}
+        onOpenChange={(open: boolean) => {
+          if (!open) projectFiles.cancelSaveNamePrompt();
+        }}
+      >
+        <DialogContent className="max-w-lg">
+          <DialogHeader>
+            <DialogTitle>{t("toolbar.item.saveProjectAsTitle")}</DialogTitle>
+            <DialogDescription>
+              {t("toolbar.item.saveProjectAsDesc")}
+            </DialogDescription>
+          </DialogHeader>
+          <form
+            className="space-y-4"
+            onSubmit={projectFiles.submitSaveNamePrompt}
+          >
+            <div className="space-y-2">
+              <Label htmlFor="save-project-name">
+                {t("toolbar.item.saveProjectFileName")}
+              </Label>
+              <Input
+                id="save-project-name"
+                autoFocus
+                placeholder={t("toolbar.item.saveProjectFileNamePlaceholder")}
+                value={projectFiles.saveNameInput}
+                onChange={(event) =>
+                  projectFiles.setSaveNameInput(event.target.value)
+                }
+              />
+            </div>
+            <div className="flex justify-end gap-2">
+              <Button
+                type="button"
+                variant="outline"
+                onClick={() => projectFiles.cancelSaveNamePrompt()}
+              >
+                {t("common.cancel")}
+              </Button>
+              <Button
+                type="submit"
+                disabled={!projectFiles.saveNameInput.trim()}
+              >
+                {t("common.save")}
+              </Button>
+            </div>
+          </form>
+        </DialogContent>
+      </Dialog>
       <Dialog
         open={projectFiles.envStripPrompt !== null}
         onOpenChange={(open: boolean) => {
diff --git a/apps/geolibre-desktop/src/hooks/useProjectFileActions.ts b/apps/geolibre-desktop/src/hooks/useProjectFileActions.ts
index 75d061fec..0df7691da 100644
--- a/apps/geolibre-desktop/src/hooks/useProjectFileActions.ts
+++ b/apps/geolibre-desktop/src/hooks/useProjectFileActions.ts
@@ -9,6 +9,7 @@ import { useTranslation } from "react-i18next";
 import { getPluginManager } from "./usePlugins";
 import { useDesktopSettingsStore } from "./useDesktopSettings";
 import {
+  browserSaveFallsBackToDownload,
   isHttpUrl,
   isTauri,
   openProjectFile,
@@ -28,6 +29,30 @@ export interface EnvStripPrompt {
   resolve: (choice: "strip" | "keep" | "cancel") => void;
 }
 
+/**
+ * A pending "name this project file" prompt, shown when Save As (or a first
+ * Save) runs in a browser that can only download under a fixed name.
+ */
+export interface SaveNamePrompt {
+  resolve: (name: string | null) => void;
+}
+
+/**
+ * Ensure a user-entered project file name carries a recognized extension,
+ * defaulting to `.geolibre.json` when none is present so the downloaded file
+ * opens cleanly again later. Falls back to the default project name when blank.
+ *
+ * @param name - The raw file name the user typed.
+ * @returns A sanitized file name ending in a project extension.
+ */
+function ensureProjectFileName(name: string): string {
+  const trimmed = name.trim();
+  if (!trimmed) return `${DEFAULT_PROJECT_NAME}.geolibre.json`;
+  return /\.(geolibre\.json|geolibre|json)$/i.test(trimmed)
+    ? trimmed
+    : `${trimmed}.geolibre.json`;
+}
+
 /**
  * Bundles every project file action (open from file/URL/recent, save, save as)
  * along with the related dialog state (Open-from-URL, env-var strip prompt, and
@@ -52,8 +77,16 @@ export function useProjectFileActions(mapControllerRef: MapControllerRef) {
   const [envStripPrompt, setEnvStripPrompt] = useState<EnvStripPrompt | null>(
     null,
   );
+  const [saveNamePrompt, setSaveNamePrompt] = useState<SaveNamePrompt | null>(
+    null,
+  );
+  const [saveNameInput, setSaveNameInput] = useState("");
   const projectUrlAbortRef = useRef<AbortController | null>(null);
   const recentAbortRef = useRef<AbortController | null>(null);
+  // Guards against overlapping saves: a second save started while a prompt
+  // dialog is open would overwrite the pending prompt and strand the first
+  // call's unresolved promise.
+  const isSavingRef = useRef(false);
 
   const handleOpenFromFile = async () => {
     const result = await openProjectFile();
@@ -222,7 +255,29 @@ export function useProjectFileActions(mapControllerRef: MapControllerRef) {
     setEnvStripPrompt(null);
   };
 
-  const saveProject = async (options?: {
+  // Ask the user to name the project file. Used only when saving falls back to
+  // a browser download (no File System Access picker), where the name is the
+  // only thing the user can control. Resolves with the name, or null if cancelled.
+  const askSaveName = (defaultName: string) =>
+    new Promise<string | null>((resolve) => {
+      setSaveNameInput(defaultName);
+      setSaveNamePrompt({ resolve });
+    });
+
+  const submitSaveNamePrompt = (event?: FormEvent<HTMLFormElement>) => {
+    event?.preventDefault();
+    saveNamePrompt?.resolve(saveNameInput);
+    setSaveNamePrompt(null);
+    setSaveNameInput("");
+  };
+
+  const cancelSaveNamePrompt = () => {
+    saveNamePrompt?.resolve(null);
+    setSaveNamePrompt(null);
+    setSaveNameInput("");
+  };
+
+  const runSaveProject = async (options?: {
     saveAs?: boolean;
   }): Promise<boolean> => {
     const { project, defaultProjectName, content, projectPath } =
@@ -247,6 +302,19 @@ export function useProjectFileActions(mapControllerRef: MapControllerRef) {
     // Save As fall back to the save dialog for them.
     const existingLocalPath =
       projectPath && !isHttpUrl(projectPath) ? projectPath : null;
+    // Browsers without the File System Access picker (Firefox, Safari) can only
+    // download under a fixed name, so Save As (and a first Save) would otherwise
+    // reuse a default name — exactly the bug users hit. Prompt for the name so
+    // they can choose it; later in-place Saves reuse the chosen name silently.
+    let saveName = `${defaultProjectName}.geolibre.json`;
+    const promptForName =
+      browserSaveFallsBackToDownload() &&
+      (options?.saveAs === true || !existingLocalPath);
+    if (promptForName) {
+      const chosen = await askSaveName(saveName);
+      if (chosen === null) return false;
+      saveName = ensureProjectFileName(chosen);
+    }
     let path: string | null;
     try {
       path =
@@ -254,7 +322,7 @@ export function useProjectFileActions(mapControllerRef: MapControllerRef) {
           ? await saveProjectFileToPath(contentToSave, existingLocalPath)
           : await saveProjectFile(
               contentToSave,
-              existingLocalPath ?? `${defaultProjectName}.geolibre.json`,
+              promptForName ? saveName : (existingLocalPath ?? saveName),
             );
     } catch (error) {
       console.error("Failed to save project", error);
@@ -276,6 +344,19 @@ export function useProjectFileActions(mapControllerRef: MapControllerRef) {
     return true;
   };
 
+  // Serialize saves so overlapping invocations cannot clobber a pending prompt.
+  const saveProject = async (options?: {
+    saveAs?: boolean;
+  }): Promise<boolean> => {
+    if (isSavingRef.current) return false;
+    isSavingRef.current = true;
+    try {
+      return await runSaveProject(options);
+    } finally {
+      isSavingRef.current = false;
+    }
+  };
+
   const handleSave = () => saveProject();
   const handleSaveAs = () => saveProject({ saveAs: true });
 
@@ -305,6 +386,11 @@ export function useProjectFileActions(mapControllerRef: MapControllerRef) {
     projectUrlLoading,
     envStripPrompt,
     resolveEnvStripPrompt,
+    saveNamePrompt,
+    saveNameInput,
+    setSaveNameInput,
+    submitSaveNamePrompt,
+    cancelSaveNamePrompt,
     handleOpenFromFile,
     handleOpenFromUrl,
     handleOpenRecent,
diff --git a/apps/geolibre-desktop/src/i18n/locales/en.json b/apps/geolibre-desktop/src/i18n/locales/en.json
index c566567b8..48141387a 100644
--- a/apps/geolibre-desktop/src/i18n/locales/en.json
+++ b/apps/geolibre-desktop/src/i18n/locales/en.json
@@ -834,6 +834,10 @@
       "open": "Open",
       "somethingWentWrong": "Something went wrong",
       "dismiss": "Dismiss",
+      "saveProjectAsTitle": "Save project as",
+      "saveProjectAsDesc": "Choose a file name. The project downloads to your browser's downloads folder.",
+      "saveProjectFileName": "File name",
+      "saveProjectFileNamePlaceholder": "my-project.geolibre.json",
       "directionsNoticeTitle": "Directions uses a public routing server",
       "directionsNoticeDesc": "Turning on Directions sends the waypoints you place to the public OSRM demo server (router.project-osrm.org) to calculate routes — your coordinates leave your device for those requests. The demo server is rate-limited and supports driving only.",
       "reverseGeocode": "Reverse Geocode",
diff --git a/apps/geolibre-desktop/src/lib/tauri-io.ts b/apps/geolibre-desktop/src/lib/tauri-io.ts
index 77d1d550c..f9df202e5 100644
--- a/apps/geolibre-desktop/src/lib/tauri-io.ts
+++ b/apps/geolibre-desktop/src/lib/tauri-io.ts
@@ -628,6 +628,24 @@ async function openProjectFileBrowser(): Promise<{
   };
 }
 
+/**
+ * Whether saving a project in the current environment would silently fall back
+ * to an anchor download under a fixed name — i.e. a browser (not Tauri) that
+ * lacks the File System Access save picker (`window.showSaveFilePicker`).
+ * Chromium browsers expose the picker and let the user name the file; Firefox
+ * and Safari do not, so callers prompt for a file name themselves before saving.
+ *
+ * @returns True only in a browser without the save picker; false under Tauri
+ *   (which uses the native save dialog) or when the picker is available.
+ */
+export function browserSaveFallsBackToDownload(): boolean {
+  if (isTauri()) return false;
+  if (typeof window === "undefined") return false;
+  return (
+    typeof (window as BrowserFilePickerWindow).showSaveFilePicker !== "function"
+  );
+}
+
 async function saveProjectFileBrowser(
   content: string,
   defaultName?: string,