diff --git a/packages/trace-viewer/src/sw/traceModelBackends.ts b/packages/trace-viewer/src/sw/traceModelBackends.ts
index 6ed16f037f..dfff79d159 100644
--- a/packages/trace-viewer/src/sw/traceModelBackends.ts
+++ b/packages/trace-viewer/src/sw/traceModelBackends.ts
@@ -23,9 +23,6 @@ const zipjs = zipImport as typeof zip;
 
 type Progress = (done: number, total: number) => undefined;
 
-const searchParams = new URL(self.location.href).searchParams;
-const testServerPort = searchParams.get('testServerPort');
-
 export class ZipTraceModelBackend implements TraceModelBackend {
   private _zipReader: zip.ZipReader<unknown>;
   private _entriesPromise: Promise<Map<string, zip.Entry>>;
@@ -33,16 +30,8 @@ export class ZipTraceModelBackend implements TraceModelBackend {
 
   constructor(traceURL: string, progress: Progress) {
     this._traceURL = traceURL;
-
-    const baseURL = new URL(self.location.href);
-    if (testServerPort) {
-      baseURL.pathname = '/trace/';
-      baseURL.port = testServerPort;
-    }
-
-    const url = new URL(formatUrl(traceURL), baseURL);
     this._zipReader = new zipjs.ZipReader(
-        new zipjs.HttpReader(url, { mode: 'cors', preventHeadRequest: true } as any),
+        new zipjs.HttpReader(formatUrl(traceURL), { mode: 'cors', preventHeadRequest: true } as any),
         { useWebWorkers: false });
     this._entriesPromise = this._zipReader.getEntries({ onprogress: progress }).then(entries => {
       const map = new Map<string, zip.Entry>();
@@ -97,7 +86,7 @@ export class FetchTraceModelBackend implements TraceModelBackend {
 
   constructor(traceURL: string) {
     this._traceURL = traceURL;
-    this._entriesPromise = this._fetchFile(traceURL).then(async response => {
+    this._entriesPromise = fetch(formatUrl(traceURL)).then(async response => {
       const json = JSON.parse(await response.text());
       const entries = new Map<string, string>();
       for (const entry of json.entries)
@@ -140,22 +129,21 @@ export class FetchTraceModelBackend implements TraceModelBackend {
     if (!fileName)
       return;
 
-    return this._fetchFile(fileName);
-  }
-
-  private async _fetchFile(path: string) {
-    const url = new URL('/trace/file', self.location.href);
-    url.searchParams.set('path', path);
-    if (testServerPort)
-      url.port = testServerPort;
-    return fetch(url);
+    return fetch(formatUrl(fileName));
   }
 }
 
+const baseURL = new URL(self.location.href);
+baseURL.port = baseURL.searchParams.get('testServerPort') ?? baseURL.port;
+
 function formatUrl(trace: string) {
-  let url = trace.startsWith('http') || trace.startsWith('blob') ? trace : `file?path=${encodeURIComponent(trace)}`;
-  // Dropbox does not support cors.
-  if (url.startsWith('https://www.dropbox.com/'))
-    url = 'https://dl.dropboxusercontent.com/' + url.substring('https://www.dropbox.com/'.length);
+  if (trace.startsWith('https://www.dropbox.com/'))
+    return 'https://dl.dropboxusercontent.com/' + trace.substring('https://www.dropbox.com/'.length);
+
+  if (trace.startsWith('http') || trace.startsWith('blob'))
+    return trace;
+
+  const url = new URL('/trace/file', baseURL);
+  url.searchParams.set('path', trace);
   return url;
 }