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).
]) {
              text = await actAndWaitForInput(
                page,
                `#\\3${Math.floor(refOpen / 10)} ${refOpen % 10}R`,
                async () => {
                  await page.evaluate(refElem => {
                    window.document
                      .getElementById(`${refElem}R`)
                      .scrollIntoView();
                  }, refOpen);
                },
                false
              );
              expect(text)
                .withContext(`In ${browserName}`)
                .toEqual(`PageOpen ${pageNumOpen}`);
              text = await page.$eval(
                `#\\3${Math.floor(refClose / 10)} ${refClose % 10}R`,
                el => el.value
              );
              expect(text)
                .withContext(`In ${browserName}`)
                .toEqual(`PageClose ${pageNumClose}`);
            }
          }
        })
      );
    });
  });
  describe("in js-authors.pdf", () => {