Title: Download completes inside StreamDL, but fails at final handoff to Firefox Downloads

Description:

I’m reporting an issue where StreamDL appears to download the video successfully inside the extension, but the download then fails at the final stage when the completed file is handed off to Firefox’s built-in Downloads system.

In the Firefox Downloads window (Ctrl+J), the download entry ends with an error. This is important because it changes the likely diagnosis: the problem does not appear to be related to site support, stream detection, or stream decryption. StreamDL seems to process the stream correctly. The failure occurs later, when the extension tries to pass the finished file to Firefox’s internal download mechanism.

This suggests the issue is likely in the integration between StreamDL and Firefox’s download API — for example, a possible race condition with Blob URL revocation, a limitation with large files/temp storage, or another problem in the final file handoff.

Steps to reproduce:

Open a page with a supported video stream in Firefox.

Use StreamDL to start downloading the video.

Wait for StreamDL to complete its internal download/processing.

Open the Firefox Downloads window (Ctrl+J).

Observe that the download entry shows an error at the final saving stage.

Expected behavior:

The completed file should be saved successfully through Firefox’s Downloads system without an error.

Actual behavior:

StreamDL completes its internal download, but Firefox shows an error for the final download/save operation.