Guide

1. Install it

State Mover is not on the extension stores yet, so you build it from source. There is no toolchain, no dependencies and no bundler.

git clone https://github.com/animeshsinghweb/StateMover.git
cd StateMover
./scripts/build.sh

That writes two ready-to-load folders into dist/:

• dist/chromium/ for Chrome, Edge, Brave, Opera and Vivaldi
• dist/firefox/ for Firefox 142 and later

Firefox's picker is a file picker rather than a folder picker, which is why you point it at the manifest inside the folder. Firefox also drops temporary add-ons when you close the browser; Chromium browsers keep an unpacked extension until you remove it.

Chromium browsers can also load the repository root directly, since manifest.json sits at the top level. Firefox cannot, because it needs manifest.firefox.json renamed into place, which is what the build step does.

2. First run

Open a normal http or https page and click the State Mover icon. The popup shows the page's origin under the title, so you always know which site you are about to read or write.

You will see two tabs, localStorage and sessionStorage, each with a count of how many keys the page has. On a fresh install nothing is ticked.

3. Picking keys

Tick the keys you want. The list is sorted alphabetically and shows each value's size, so a heavyweight key is obvious at a glance. Sizes are counted the way the browser counts them against the origin's storage quota, which is two bytes per character, so they line up with the 5 MB ceiling a page actually has.

• Filter narrows the list as you type. Handy on pages with a hundred keys, which is more common than you would think.
• All ticks everything currently visible. With a filter active it ticks only the matches, so auth then All grabs every auth key and nothing else.
• None clears the current tab's selection.

The running total under the list tells you how many keys are selected across both tabs and how large the snapshot will be. Refresh next to it re-reads the page, which is useful after the app has written something while the popup was open.

The popup remembers the key list for each site, so reopening it paints straight away and refreshes in the background. While that is happening it says so under the list. If the page is too busy to answer, the remembered list stays on screen with a Retry, rather than the popup going blank.

Your selection is saved automatically, per origin. Tick three keys on app.staging.example.com and they will still be ticked next time you open the popup there, without affecting what you picked on production.

4. Previewing a value

Click the ▶ at the right of any row to expand it. The value appears underneath, pretty-printed if it parses as JSON and shown verbatim otherwise.

Values are fetched only at that moment. Opening the popup reads key names and sizes and nothing else, which keeps things quick on pages holding megabytes of state.

5. Exporting

With at least one key ticked, both export buttons light up.

• Copy snapshot puts the JSON on your clipboard and tells you how large it was.
• Download .json saves it as state-mover-<host>-<timestamp>.json, which is useful when you want to keep a known-good state around rather than paste it straight away.

6. Importing

Switch to the target tab and open the popup there. Paste the snapshot into the import box, or use Load file... to pick a downloaded .json.

Apply snapshot writes the values. With Reload the page after import ticked, which it is by default, the tab refreshes so the app picks up the new state immediately. Untick it if you would rather reload yourself, or if you want to import into several storages before refreshing.

7. The snapshot format

A snapshot is plain JSON, readable and editable by hand:

{
  "__localStorageTransfer__": true,
  "version": 2,
  "origin": "https://app.example.com",
  "exportedAt": "2026-08-25T10:15:00.000Z",
  "local":   { "currentUser": "{\"id\":42}" },
  "session": { "tempState": "{\"step\":3}" }
}

Values are strings, because that is exactly how the browser stores them. A JSON object living in localStorage arrives as an escaped string, which is correct and what the app on the other side expects to parse.

The origin and exportedAt fields are informational. Nothing stops you applying a snapshot to a different origin, which is the entire point.

Snapshots written by version 1.1, which put localStorage values in a flat data field, still import correctly.

8. When something does not work

"State Mover can only read http and https pages"

You are on a page no extension may touch: chrome://, edge://, about:, an add-on store, or a local file. This is a browser rule, not a State Mover limitation. Open a regular site.

The key list is empty

The page genuinely has no keys in that storage, or it was still loading when you opened the popup. Close and reopen the popup to re-read.

"Storage quota exceeded"

The target origin is at its storage limit, usually around 5 MB per origin. Clear some keys on the target and apply again.

The app still shows the old state after import

Reload the page. If you unticked the reload option, nothing has told the app that storage changed. Some apps also cache state in memory at startup, in which case a hard reload helps.

Nothing happens on a page you control

A few sites block storage access from injected scripts through their content security policy or a sandboxed context. State Mover reports what it can, but it cannot get around a page that refuses to hand over its storage.

Working out where the time went

The status line under the key list shows the version and how long the last load took. Hover it for a breakdown by step. Reading storage means running a snippet inside the page, so if read the page dominates, the page is busy and there is nothing the extension can do to hurry it - though the remembered list means you are not staring at an empty popup while it finishes.

"This page is not responding"

State Mover reads storage by running a snippet inside the page, so a page whose main thread is tied up cannot answer until it frees up. Rather than sit there, the popup gives up after a few seconds and offers Try again. Heavy pages under load, and pages still loading, are the usual causes.

"The browser unloaded this tab to free memory"

When a lot of tabs are open, Chromium discards the ones you are not looking at to reclaim memory. A discarded tab has no page left to read, so there is nothing for State Mover to inject into. The popup offers Reload the tab, which brings the page back and reads it once it is up.

9. A word on tokens

Session tokens are the most useful thing to move and the most sensitive. A snapshot containing one is, for practical purposes, a copy of that session.

• Treat a downloaded snapshot the way you would treat a password. Do not commit one to a repository or paste it into a shared channel.
• Applying a production token to a local build gives that build production access. That is often exactly what you want, and occasionally exactly what you do not.
• Clear the import box when you are done if you are screen sharing.

State Mover never transmits any of this. Where a snapshot goes after it reaches your clipboard is entirely up to you.