A Firefox extension that adds a price history panel to eBay search pages. Select listings to plot their sale prices — sold listings are charted by sale date; active listings are shown in a price-distribution view.
Supports all major eBay sites: ebay.com, ebay.co.uk, ebay.de, ebay.ca, ebay.com.au, ebay.fr, ebay.it, and ebay.es.
- Scatterplot panel docked to any edge of the screen (top, right, bottom, left)
- Per-listing checkboxes to choose which items to include in the chart
- "Plot all" checkbox to select or deselect all valid listings at once
- Drag to redock — drag the panel header or the toggle tab to move the panel to a different edge
- Resizable — drag the panel's free edge to expand or contract it
- Currency conversion — choose a display currency from the panel header; all prices are converted from their original listing currencies using live exchange rates
- Best Offer warning — sold listings that had Best Offer enabled are marked, since eBay shows the asking price, which may not be what the item sold for
- Dark / light theme — toggle in the panel header
- Adjustable text size — set the panel font size from the header
- Persists across page loads — selected items, dock position, panel open/closed state, theme, and font size are saved in
localStorage - Handles infinite scroll and pagination automatically
This extension is not listed on AMO, so it must be loaded manually as a temporary add-on.
Prerequisites: Firefox, Node.js (for npm)
- Clone or download this repository
- Run
npm install(installs Chart.js and easy-currencies plus dev tooling, and vendors them intovendor/) - Open Firefox and go to
about:debugging#/runtime/this-firefox - Click Load Temporary Add-on and select
manifest.jsonfrom this folder
The extension will remain active until Firefox is closed. Repeat step 4 after restarting.
- Go to any eBay search page — the 📈 tab appears on the edge of the screen
- Click the 📈 tab to open the price history panel (or check a listing to open it automatically)
- Check the Plot box on any listing to add it to the chart
- Use Plot all to select everything on the page at once
- Hover over a point on the chart to see the item title and price
Sold vs. active listings: Sold listings are charted by sale date. Active (unsold) listings appear in a separate "Active Listings" strip chart sorted by price — the x-axis spreads items horizontally so price clusters are visible. Both chart sections appear in the same panel when you have both types selected.
Best Offer listings: If a sold listing had Best Offer enabled, a warning appears under its Plot box. eBay shows the seller's asking price on these cards, but if the seller accepted an offer the item actually sold for less — and the search page doesn't say which happened. Open the listing to see the real figure. Active listings don't get the warning: their price is simply what the seller is asking.
Across pages: Your selections are saved, so you can move to the next page of results and keep adding listings — the chart accumulates points from every page you visit.
Moving the panel: Drag the "Price History" header to any edge of the screen. Release near an edge to snap it there. Close the panel with the × button — a small tab appears to reopen it. The tab can also be dragged to a different edge.
Resizing: Hover over the panel's inner edge until the cursor changes, then drag to resize.
Theme and text size: Use the header controls to switch between dark and light mode (☉/☾) and to set the panel's text size. Both preferences are saved and restored on your next visit.
Currency conversion: The panel header includes a currency dropdown (USD, GBP, EUR, CAD, AUD, MXN). It defaults to the native currency of the eBay site you're on. Changing it converts all charted prices on the fly using live exchange rates; your selection is saved and restored on your next visit.
No build step is needed to develop. After editing any file in src/:
- Go to
about:debugging#/runtime/this-firefox - Find the extension and click Reload
Run the unit tests with npm test (covers extraction, storage, dock geometry, chart math, currency conversion, checkbox state, panel header wiring, and the startup sequence).
Code style is handled by Prettier — run npm run format after editing. npm run lint checks the extension against Firefox Add-on policies, not code style.
To package the extension for distribution, run npm run lint and npm run build.
See ARCHITECTURE.md for a full explanation of how the extension works.