Chrome
The Chrome Web Store is the direct install path. Add AttachDock, refresh Gmail, and the dock will be ready inside Gmail.
Install for ChromeInstall AttachDock
AttachDock works inside desktop Gmail after you install the extension. Choose the path that matches your browser.

Manual install paths
The Chrome Web Store is the direct install path. Add AttachDock, refresh Gmail, and the dock will be ready inside Gmail.
Install for ChromeEdge can install Chrome Web Store extensions. If Edge asks, allow extensions from other stores, then install AttachDock and refresh Gmail.
Install for EdgeOpera is Chromium-based, so the Chrome Web Store listing works here too. Install AttachDock, then refresh Gmail.
Install for OperaIf your desktop browser can install Chrome Web Store extensions, open the listing and refresh Gmail after installation.
Open Chrome Web StoreAttachDock for Safari is available from the Mac App Store. Install the Mac app, enable the Safari extension, then refresh Gmail.
Open Mac App StoreAdd AttachDock to your desktop browser.
Open an email with attachments, then click AttachDock inside Gmail.
Choose a My Drive folder and save a copy.