Reverse-engineering the chrome extension, not to be confused with the GApps App to work in Firefox in addition to Chrome.
Unfortinuately, I'm not sure how possible this is to get completely working. https://github.com/InboxSDK/InboxSDK, which this extension uses, doesn't appear to support Firefox out of the box.
Support would probably have to be added there.
Works:
- Embedded frame in the Gmail window
Doesn't:
- "Add to Todoist" button is missing, InboxSDK isn't loading for some reason (seach TODO in InboxSDK)
- Loading temporary extensions: https://extensionworkshop.com/documentation/develop/temporary-installation-in-firefox/
- Downloading CRX files: https://chrome.google.com/webstore/detail/crx-extractordownloader/ajkhmmldknmfjnmeedkbkkojgobmljda