You can fix it by going to "Reading & Display" in the Preferences.
Look for the option "Open Messages in" and change it to "New message window".

The to hide the tabs, go to the config editor and look for "mail.tabs.autoHide", set it to "true".

Done.

Android Market still feels like a rough beta-version due to two big reasons.

* Paid applications is _still_ not released in many countries.

* Way too much spam, hidden advertisement or illegal content.

More apps is not the solution, better quality is.