Steam Bulk Sell per k5md

Steam Bulk Sell is a web-extension for Firefox to help selling multiple inventory items at once. It allows one to select multiple items, use prices presets (median, median * multiplier, custom) and sell them.
- Requires permissions for Steam inventory pages
- Permissions for contextualIdentities, cookies and webRequest, and webRequestBlocking are introduced to support cookie-isolating addons - see this issue.
- Allows to select whole inventory tab at once
- Prices are loaded asynchronously - just open sell modal once and the extension will start fetching prices for currently checked items, close modal and continue selecting/deselecting items
- Prices are fetched from Steam, so expect ~1s delay between requests, ~2s delay for each selling action
- Open source - feel free to contribute!