## Issue
- The previous code does detect uploads from multiple tabs, but it was done by handling the CONFLICT error message from the backend. At certain corner-cases, this does not work well. A better way is to not allow resumption while the same file is being uploading from another tab.
- When an upload from 1 tab finishes, the GUI on the other tab does not remove the completed item. User either have to refresh or click Cancel. Clicking Cancel results in the 404 backend error. This should be avoided.
## Approach
- Added tab synchronization and locking by passing the "locked" and "removed" information through `localStorage`.
## Other considered approaches
- Wallet sync -- but decided not to pollute the wallet.
- 3rd-party redux tab syncing -- but decided it's not worth adding another module for 1 usage.
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