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).
.withContext(`In ${browserName}`)
            .toEqual("visible");
          
          await clearInput(page, "#\\34 16R");
          
          await page.click("#\\34 19R");
          await page.waitForFunction(
            `getComputedStyle(document.querySelector("#\\\\34 27R")).visibility !== "visible"`
          );
          visibility = await page.$eval(
            "#\\34 27R",
            el => getComputedStyle(el).visibility
          );
          expect(visibility).withContext(`In ${browserName}`).toEqual("hidden");
        })
      );
    });
    it("must format the field with 2 digits and leave field with a click", async () => {
      await Promise.all(
        pages.map(async ([browserName, page]) => {
          await page.type("#\\34 16R", "3.14159", { delay: 200 });
          await page.click("#\\34 19R");
          const text = await page.$eval("#\\34 16R", el => el.value);
          expect(text).withContext(`In ${browserName}`).toEqual("3,14");
          const sum = await page.$eval("#\\34 27R", el => el.value);
          expect(sum).withContext(`In ${browserName}`).toEqual("3,14");
        })
      );
    });
    it("must format the field with 2 digits, leave field with a click and again", async () => {