When multiple urls are passed to conkeror on the command line, a timing bug that exists in both tab-bar
and new-tabs results in an error like the following:

  Console error: [JavaScript Warning: "reference to undefined property b.tab" {file:
"chrome://conkeror/content/tab-bar.js" line: 106}]
  Category: chrome javascript

This problem only seems to exist on initial launch.

To reproduce:

  conkeror -q -e 'url_remoting_fn = load_url_in_new_buffer;' -e 'require("tab-bar.js");' about:blank
about:blank

or:

  conkeror -q -e 'url_remoting_fn = load_url_in_new_buffer;' -e 'require("new-tabs.js");' about:blank
about:blank