The logs
```
  Stack:
    Error: Protocol error (Target.createTarget): can't access property "closing", selectedTab is null _setPositionalAttributes@chrome://browser/content/tabbrowser-tabs.js:1123:11
    _insertTabAtIndex@chrome://browser/content/tabbrowser.js:3286:25
    addTab@chrome://browser/content/tabbrowser.js:2710:16
    addTab@chrome://remote/content/shared/TabManager.jsm:24:31
    createTarget@chrome://remote/content/cdp/domains/parent/Target.jsm:90:28
    execute@chrome://remote/content/cdp/domains/DomainCache.jsm:101:25
    execute@chrome://remote/content/cdp/sessions/Session.jsm:64:25
    onPacket@chrome://remote/content/cdp/CDPConnection.jsm:248:36
    onMessage@chrome://remote/content/server/WebSocketTransport.jsm:89:18
    handleEvent@chrome://remote/content/server/WebSocketTransport.jsm:71:14
    openPromptSync@resource://gre/modules/Prompter.jsm:1057:17
    alert@resource://gre/modules/Prompter.jsm:1329:17
    alert@resource://gre/modules/Prompter.jsm:80:7
    _displayPrintingError@chrome://global/content/printUtils.js:572:21
```
My feeling is that something is wrong with the printing test and an alert is generated which blocks following attempts to get the current selected tab (see https://searchfox.org/mozilla-central/source/toolkit/components/printing/content/printUtils.js#572).
const text = await page.$eval("#\\35 6R", el => el.value);
          expect(text).withContext(`In ${browserName}`).toEqual("0,0,1,1,1");
        })
      );
    });
    it("must check display", async () => {
      await Promise.all(
        pages.map(async ([browserName, page]) => {
          for (const [type, vis] of [
            ["hidden", "hidden"],
            ["noPrint", "visible"],
            ["noView", "hidden"],
            ["visible", "visible"],
          ]) {
            let visibility = await page.$eval(
              "#\\35 6R",
              el => getComputedStyle(el).visibility
            );
            await clearInput(page, "#\\35 5R");
            await page.type(
              "#\\35 5R",
              `this.getField("Text2").display = display.${type};`
            );
            await page.click("[data-annotation-id='57R']");
            await page.waitForFunction(
              `getComputedStyle(document.querySelector("#\\\\35 6R")).visibility !== "${visibility}"`
            );
            visibility = await page.$eval(
              "#\\35 6R",
              el => getComputedStyle(el).visibility