Update faf README with content command and troubleshooting

- Document new 'content' command for fetching HTML from tabs
- Add troubleshooting section for HTTP endpoint issues
- Add instructions for running from Nix development shell
- Note requirement for 'nix develop -c $(which fish)'

scripts/f-around-firefox/README.md

@@ -6,17 +6,59 @@ Get information about Firefox's open tabs from the command line.
 
 ```bash
 faf [method] [rdp_port]
+faf content <tab-id> [rdp_port]
 ```
 
 **Methods:**
 - `session`, `s` - Read from Firefox session files (default)
 - `rdp`, `r` - Use Remote Debugging Protocol
 - `both`, `b` - Try both methods
+- `content`, `c` - Get HTML content from a tab via WebSocket
 
 **Examples:**
 ```bash
 faf                    # Use session files (default)
 faf rdp                # Use RDP on default port 6000
 faf rdp 9222           # Use RDP on port 9222
+faf content 123        # Get HTML from tab 123 (port 6000)
+faf content 123 9222   # Get HTML from tab 123 (port 9222)
 ```
 
+## Content Command
+
+The `content` command connects to a Firefox tab via WebSocket using the Remote Debugging Protocol and retrieves the rendered HTML content. This enables agentic workflows where you can query webpages you have open in Firefox.
+
+**Requirements:**
+- Firefox must be running with remote debugging enabled
+- The tab must be debuggable (most regular web pages are, but `about:` pages may not be)
+- The `websockets` Python library must be available
+
+**Output:**
+The command outputs raw HTML to stdout, making it easy to pipe to other tools:
+```bash
+faf content 123 | grep "some-text"
+faf content 123 > page.html
+```
+
+## Troubleshooting
+
+### HTTP Endpoint Not Responding
+
+If you see "Remote end closed connection without response" errors even though Firefox shows DevTools is connected (indicated by the browser being "under remote control" in the address bar), this is a known issue that needs investigation. The WebSocket connections may work even when the HTTP `/json/list` endpoint doesn't respond properly.
+
+**Workaround:** Try using the `content` command directly if you know the tab ID, or use the session file method to list tabs.
+
+### Running from Nix Development Shell
+
+If the `websockets` library is not available in your system Python, you can run the script from the Nix development shell:
+
+```bash
+cd scripts/f-around-firefox
+nix develop -c $(which fish)
+python3 faf.py rdp
+# or
+python3 faf.py content <tab-id>
+```
+
+**Note:** Use `nix develop -c $(which fish)` to properly enter the shell with fish. This ensures the script has access to all required dependencies including `websockets` and `lz4`.
+