DownloadBar

A small MV3 extension that restores a Chrome-style download shelf across the bottom of every page. No build step, no framework, no dependencies.

Chrome/Edge: https://chromewebstore.google.com/detail/downloadbar/idiafamnhiaagbjaboimogfnedchpfjo

Firefox: https://addons.mozilla.org/en-US/firefox/addon/downloadbar_/

Goals

• Reproduce the classic Chromium download shelf as closely as the extension APIs allow.
  • Smooth over rough edges in the old implementation where needed -- "rose tinted glasses" approach.
• Show the same bar in every tab, updating in real time.
• Cost effectively nothing while idle.

Non-goals

• Modifying browser chrome (impossible from an extension).
• Replacing the new downloads bubble (we coexist with it).
• Anything out of scope for a modern extension
  • We cannot auto-open files without user input. See "Notify-on-complete" below.
  • We cannot inject HTML on chrome:// pages or any other internal page.
  • The native chrome chip menu went down (below the window). We are popping up because we can't draw content outside of the DOM.

Key files

background.js is the only piece that talks to the underlying chrome.downloads APIs. content.js runs on every tab, and hands state from the background service worker to the front-end ui.js. Some user actions also flow backwards to the background SW. ui.js owns the bar lifecycle and reconciles Chip instances against each broadcast. chip.js owns one chip's DOM and per-chip event wiring. menu.js is responsible for the popup menu on each download "chip". settings.js manages the persistent user settings, and is loaded by the service worker and the options UX. All other files should be self-explanatory.

Non-obvious code

• We keep a set of "visible chip IDs" to track which downloads are in progress. This survives the service worker's 30s sleep timeout.
• Each download chip should flash on completion, so we keep track of when we first flashed it, to avoid a re-flash and to smoothly resume the animation if needed.
• Icons are fetched asynchronously, but cached. On the hot path, we are in the middle of a download and need to return the icon to render without causing lag. If an icon is missing, we defer (and show nothing). Icons come from chrome.downloads.getFileIcon.
• Our download bar is injected as a top-level div ("shadow") on the DOM. We have to do some agressive CSS styling to protect it from other attributes on the host -- this download bar needs to work on any tab. This unfortunately means all of our actual CSS styling needs to be !important.
• While a download is live, we keep the SW alive with a ping every 500ms. This is needed so we draw download progress correctly, and take download completion actions correctly.

Notify-on-complete

The classic shelf had two related affordances that auto-opened a finished download with the OS default handler:

• Open when done -- per-download toggle on an in-progress chip (could also be triggered by clicking on a chip).
• Always open files of this type -- per-extension persistent rule; on completion the chip was silently removed and the file launched in its OS default handler.

Neither is feasible in a modern extension. chrome.downloads.open() can only be called when the originating gesture was from the user. Even when the user directly clicks on a file, it still triggers a confirmation dialogue, so a silent download is not possible.

Instead, we built a feature that's basically the same -- notify the user when the download is done. We can easily flash the taskbar on complete (and do nothing when chrome is active).

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Future work

• Persistence across restarts. On SW boot, rehydrate chips from chrome.downloads.search. Option to restore everything recent vs. only interrupted/paused downloads with canResume: true.
• Grouping. When several downloads arrive from the same origin within a few seconds (image-savers, "download all"), collapse them into a single expandable chip. Both the classic shelf and the new bubble flood badly in this case.
• Pinning. Right-click -> pin a chip; survives auto-dismiss and "clear all". For the "I'll deal with that installer in a minute" case.
• Notification fallback. Optional chrome.notifications.create on completion when Chrome is unfocused, in addition to (or instead of) the taskbar flash. Useful on platforms where flash semantics are weak.
• Source-tab jumpback. Clicking a chip in a tab other than the one that started the download could optionally switch focus back to the originating tab instead of (or before) opening the file.
• Hash display. Menu option to compute SHA-256 of a completed file. Requires the user to enable "Allow access to file URLs" on the extension; then fetch('file:///' + item.filename) -> crypto.subtle.digest. Gate the option on file size to avoid hashing multi-GB ISOs synchronously, or implement a streaming hasher.