Wallets & Self-Custody How Browser Extensions Isolate Poker Site Data Owen Gaines Owen Gaines is a professional poker player and author who has played an estimated ten million hands and written four poker strategy books. September 29, 2026 Modern browsers isolate websites from one another by design. A poker site cannot read your exchange session, and a malicious page cannot read the poker cashier. Browser extensions are the exception to that model. An extension with broad permissions can see and modify every page you visit, including the deposit address shown in a cryptocurrency cashier. For crypto poker players, this matters more than for most users because the browser often holds both halves of a transaction: the site that displays a deposit address and the wallet extension that signs the transfer. Understanding how extension isolation works, and where it stops, determines whether your browser is a controlled environment or an open door. This guide explains how browsers separate site data, how extensions and wallet extensions cross those boundaries, and how players structure browser use so a single compromised extension can’t redirect a deposit. How Browsers Separate Site Data Two mechanisms keep websites apart. The same-origin policy prevents a page from reading data belonging to a different origin (the combination of scheme, domain, and port). Site isolation, standard in Chromium-based browsers and implemented in Firefox, goes further by running different sites in separate operating-system processes, so a compromised page can’t read another site’s memory. Cookies, local storage, and session tokens are scoped to their origin as well. Your poker account session is readable only by the poker site’s own pages. These protections govern websites. Extensions sit above them: once installed and granted access, an extension operates with privileges the browser deliberately denies to web pages. That is why extension choices, not site behavior, are usually the weak point in browser security. How Extensions Cross Site Boundaries Isolated Worlds and the Shared DOM Extensions interact with pages through content scripts. By default, a content script runs in an “isolated world”: it has its own JavaScript environment, so the page can’t access the extension’s variables and the extension can’t directly access the page’s. Both, however, share the DOM, the rendered page structure. A content script can read any text on screen, including a displayed deposit address or balance, and can rewrite it. Host Permissions Which pages a content script can touch is set by host permissions in the extension’s manifest. An extension requesting access to all URLs appears in Chrome as “Read and change all your data on all websites.” Chromium browsers let you restrict this to specific sites or to activation on click, and Firefox offers similar per-site controls. Restricting access is the single most effective isolation step available to users. Extension Storage and Key Custody Each extension has its own storage that other extensions and websites can’t read. Wallet extensions keep private keys there, encrypted with your password. The keys are protected from websites and other extensions, but not from malware on the device or from a malicious update to the wallet extension itself. What This Means for Wallet Extensions and Poker Cashiers The permission level you grant determines what an extension can see during deposits and withdrawals: Site Access Setting What the Extension Can Access Risk During Cashier Use All sites Read and modify every page, including cashier pages High: can read balances or replace a displayed address Specific sites only Only listed domains Low, if the poker and exchange domains are excluded On click Current tab, only after you activate it Low: no access unless you trigger it Clipboard permissions Read or write copied text High: can swap a copied address before you paste Settings vary slightly between browsers, but the principle is constant: the fewer extensions with access to cashier and wallet pages, the smaller the attack surface. Deposit processing is irreversible once a transaction is broadcast, so a swapped address can’t be undone after the fact. Common Mistakes Players Make Running coupon, ad-blocking, or screenshot extensions with all-site access in the same profile used for poker cashiers and wallets Installing a wallet extension from a search ad or lookalike store listing instead of the developer’s verified link Approving every site connection request, leaving old sites able to see wallet addresses and request signatures Checking only the first and last characters of a pasted address, which clipboard hijackers specifically imitate Wallet Extension Architecture and Its Limits Provider Injection and Site Connections Ethereum-compatible wallet extensions inject a provider object into web pages so sites can request accounts and signatures. A site sees nothing until you approve a connection, and every transaction requires confirmation in the wallet’s own popup. The connected-sites list is an access-control list you should audit and prune regularly. Signatures and Token Approvals The wallet popup is the last trusted checkpoint, but only if you read it. Token approvals and off-chain permit signatures can authorize a contract to move funds later, often without an obvious transfer at signing time. Unlimited approvals remain valid until revoked. A deposit to a poker site should be a plain transfer; any request for an approval deserves scrutiny. Supply-Chain Risk in Extension Updates Extensions update automatically. A legitimate extension can be sold to a new owner or have its developer account compromised, then push malicious code to existing users with the permissions already granted. This is why a long-installed, trusted extension is not permanently safe. A Deposit Address Swapped in the Browser A player copies a Bitcoin deposit address from a cashier page in a browser profile that also runs a recently updated productivity extension. Extension permissions: all sites plus clipboard write, granted months earlier Update: pushed silently after the extension changed ownership Behavior: replaces any copied string matching a crypto address format with a lookalike address Transaction: sent from a hardware wallet that displays the destination on its own screen The Technical Process The player copies the address, and the extension’s content script overwrites the clipboard with an attacker address sharing the first four and last four characters. The player pastes into the wallet app. Before approving, they compare the full address on the hardware wallet screen against the one shown in the cashier and find the middle characters don’t match. The Outcome The transaction is cancelled before broadcast, so no funds are lost. The hardware wallet screen, which the extension can’t reach, was the independent check. Had the player confirmed on a software wallet within the same compromised profile, the swapped address could have received the deposit with no recovery path. How Professionals Separate Poker and Wallet Activity Experienced players treat the browser as several environments rather than one. They use a dedicated browser profile for poker cashiers, exchanges, and wallet extensions, with no other extensions installed. Technical Risk Management They verify every destination address on a hardware wallet screen, review extension permissions after updates, revoke unused token approvals, and disconnect old sites from their wallet. Many use the downloadable ACR Poker software for play, which keeps game sessions outside the browser’s extension ecosystem entirely. System Optimization They save verified cashier and withdrawal addresses in the wallet’s address book, which removes clipboard use from routine deposits. Technical Evolution in Browser Wallet Security Browser vendors continue narrowing extension capabilities, with stricter manifest rules, per-site access controls, and store review. Wallets are adding transaction simulation that shows what a signature will actually do before you approve it. These changes reduce risk but don’t remove the core trade-off: convenience inside the browser means trusting every extension with access to that page. Isolation you configure yourself remains the most reliable control. Frequently Asked Questions Can a browser extension see my poker account data? Yes, if it has host permissions for the poker site’s domain. An extension with access to all sites can read everything displayed on a page, including balances and deposit addresses, and can modify what you see. Restrict extensions to specific sites or on-click access, and keep poker and wallet activity in a profile without unnecessary extensions. Can other extensions access my wallet extension’s private keys? No. Each extension’s storage is isolated, and wallet extensions encrypt keys with your password. The realistic risks are different: a malicious extension altering pages or the clipboard, malware on the device, a fake wallet extension, or a compromised update to the wallet itself. Hardware wallets remove the key from the browser entirely. What does “read and change all your data on all websites” mean? It means the extension can run scripts on every page you open. Those scripts can read text, forms, and displayed data, and rewrite page content. Many legitimate extensions request this for convenience. For crypto users, it should be limited with the browser’s site access controls so the extension cannot run on cashier, exchange, or wallet pages. Does incognito mode protect me from extensions? Partially. Most browsers disable extensions in private windows unless you explicitly allow them, which reduces exposure. But private windows also clear session data and may not have your wallet extension available. A dedicated browser profile with only the extensions you need is a more practical long-term setup for poker and wallet activity. How do I detect clipboard address swapping? Compare the full pasted address with the source, including middle characters, since attackers generate lookalikes that match the start and end. The strongest check is confirming the address on a hardware wallet screen, which browser extensions cannot modify. Saving verified addresses in your wallet’s address book avoids the clipboard for repeat deposits. Should I disconnect my wallet from sites I no longer use? Yes. A connected site can see your wallet addresses and request signatures without asking to reconnect. Removing unused connections limits exposure if a site is later compromised. Also review token approvals in a block explorer or revocation tool, since approvals persist independently of the site connection and can allow contracts to move tokens.