u/iamstanty

I built Tabtwinsy because every browser treats windows as separate islands. Open a second window and the two drift apart until the tab you want is always in the other one. Arc solved this with Spaces, nothing else really did, so I wrote it as an MV3 extension.

What it does: mirrors tabs and tab groups across every normal window. Add a tab anywhere and it appears everywhere, close it anywhere and it closes everywhere, open a brand new window and it arrives already populated instead of empty. One click on the toolbar icon turns it off.

Since this sub is mostly people who build these, the interesting part was not the mirroring. It was how much of the code ended up being refusals. A tab mirror is an amplifier: any misread of browser state becomes N duplicated or N deleted tabs across someone's windows. So it will not touch the tab you are looking at, anything playing audio, or a video call page, and no single sync pass is allowed to remove more than a fraction of a window's tabs. That last guard caught a real data-loss bug during testing.

Two MV3 things that cost me days:

1. The service worker sleeps constantly, so every piece of state has to survive a restart mid-operation. Window signatures live in chrome.storage and get reloaded on wake. A subtler one: enabled defaulted to true for the few milliseconds between worker wake and the storage read, so a perfectly timed event could sync while the extension was toggled off.

2. Chromium forks are not Chrome. I built against Dia, which backs its favorites with hidden tabs that are indistinguishable from ordinary tabs through the extensions API, and which keeps invisible zero-size windows holding old tabs. Both got faithfully mirrored into every window until I gave up identifying them by their properties and started detecting them by their behavior instead (a tab that teleports between windows three times in two minutes is not a user doing that).

Free, no account, no servers, no network requests at all. Works in Chrome and other Chromium browsers.

Store: https://chromewebstore.google.com/detail/idphljlhhddadnmbnjfdmllgknfnbodn

Issues: https://github.com/stanty522/tabtwinsy

Happy to answer anything on the MV3 side.

we send campaign texts from an internal CRM. all registered, opt-outs handled. still got filtered.

added a 200/hour cap and 18 seconds between messages and it got better. but i changed the sending path at the same time, so i never worked out which one did it.

has anyone tested the throttling on its own?

Built an agent that lives in group chats. Started on Sendblue for iMessage, hit their free-plan rule where recipients have to verify before the bot is allowed to message them, paid up to remove that for groups. Added Telegram and SMS as fallbacks, then Linq as a fourth because it does iMessage, RCS and SMS through one API.

Is anyone reaching users reliably on a single channel, or is stacking providers just what this is?