Base64 Encoder Decoder Offline 作成者: v9

Base64 Encoder Decoder Offline converts text to Base64 and decodes Base64 back to readable Unicode text directly inside Firefox.

• Encode plain text to Base64.
• Correctly handle Unicode text, accented characters, and emoji.
• Decode valid Base64 into readable text.
• Detect malformed Base64 and display a clear error.
• Copy the processed result to the clipboard.
• Clear the workspace with one click.
• Work completely offline.
• Require no registration or account.

1. Click the Base64 Encoder Decoder Offline icon on the Firefox toolbar.
2. Type or paste content into the input field.
3. Click Encode to convert the text to Base64.
4. Click Decode to convert valid Base64 back to text.
5. Click Copy Result to copy the output.

The extension converts text through UTF-8 before creating Base64. This allows it to process international characters and emoji instead of being limited to basic ASCII text.


Base64 is an encoding format, not encryption. Base64 content can be decoded by anyone and should not be used to protect passwords, private keys, or confidential information.


Base64 Encoder Decoder Offline does not collect, save, log, transmit, sell, or share entered content or results.

The extension processes only content manually entered or pasted into the popup. It does not read websites, local files, open tabs, browser history, cookies, saved logins, or account data.


The extension requests no website permissions and uses no content scripts, background scripts, remote code, analytics, advertisements, or external APIs.

Clipboard access occurs only when the user clicks the copy button.


All conversion operations are performed locally inside Firefox. No Internet connection is required.