CodeMirror PRIMARY Bridge — Nicolas Hainaux

On Linux/BSD, CodeMirror-based editors (GitHub Gist, codemirror.net, and others) don't propagate text selections to the X11/Wayland PRIMARY buffer. The result: middle-click paste from those editors silently does nothing. This extension restores that workflow.

How it works

A content script watches the selection inside CodeMirror editors on allowlisted sites. When the selection changes, it sends the text to a small Python "native messaging host" running outside the browser, which
writes it to PRIMARY via xsel, xclip, or wl-copy.

Two-part install

1. The extension itself (this page).
2. A small Python helper, installed separately by running install.sh from the source tree. WebExtension APIs cannot reach clipboard tools directly — the helper is required and AMO cannot install it for you.

Full instructions, including the source repository, are at https://gitlab.com/nicolas.hainaux/cm_primary.

Security model

Off everywhere by default. The extension only forwards selections on hostnames you explicitly add to the allowlist in the options page — no allowlist entry, no message to the helper, no write to PRIMARY.

This mirrors the conservative choice Firefox made after CVE-2023-6208, which was patched by dropping all JavaScript-driven PRIMARY updates. This extension reopens that path only on sites you've explicitly trusted.

Privacy

No telemetry, no analytics, no remote servers. Selections are only forwarded to your local PRIMARY buffer.

Supported platforms

Linux X11 (tested with xsel). BSD and Wayland support is implemented but untested — feedback welcome.