RetroInbox is coming to the Chrome Web Store. Until then you can install it yourself in about two minutes, with the same 7-day free trial. You need Google Chrome on a computer (Windows, Mac, Linux or Chromebook).
Use the button above. The file RetroInbox.zip goes to your Downloads folder.
On Windows: right-click RetroInbox.zip, choose Extract All…, then Extract. On a Mac: double-click the file. You get a folder named RetroInbox.
Move that folder somewhere it can stay, for example Documents. Chrome runs RetroInbox from this folder, so do not delete it.
Copy this address, paste it into the Chrome address bar and press Enter. (Websites cannot open this page with a link.)
Use the switch in the top right corner of the extensions page.
Select the RetroInbox folder from step 2 (the one that contains manifest.json) and click Select Folder. RetroInbox appears in the list.
Click the puzzle-piece icon next to the address bar, then the pin next to RetroInbox. Open Yahoo Mail: the ads are gone and the classic look is there. The RetroInbox button has the theme, language and other options.
When a new version is out, a small red 1 appears on the RetroInbox button, and its menu shows a Download button.
RetroInbox folder and replace the old ones.chrome://extensions, click the round arrow ↻ on the RetroInbox card. Your settings and your license stay as they were.Do not remove RetroInbox to update it: removing it also removes your license from this computer. If you do need to remove it, open its menu first and click Release the license, so you can activate your key again afterwards.
chrome://extensions and switch RetroInbox back on.manifest.json.