UNIX and Linux Applications

Somehow things went all wrong with my Thunderbird's (4.0) Layout. I cannot get back to the display layout I had originally after installing. The current layout is "wide" and the "custom" layout is identical. The original looked a bit like the layout of the composition window but was a bit different but I don't recall exactly how. I have fiddled and diddled and the only place that comes close to solving it (but doesn't) is View > Layout.
4.6 allowed for one to display the source and then one could close the window and be back to the display layout but I can't do that any more either.
Help as always is appreciated.
PS the Thunderbird site was of no use.

I use Thunderbird. I would have thought that View->Layout->Classic View with the Message Pane checked would have got you back to where you wanted to be.

Thunderbird is currently at version 7.0.1. Why not just upgrade to 7.0.1. This will restore the default layout.

The problem was resolved when recently I accidentally move the cursor and struck the button which was very fortuitous and moved the "unified folders" to the right. Apparently I had buried them to the left by the reverse action again without realizing it which led to further actions. It is amazing that no one on the design team had not caught that as one would think they would've tested that action beforehand. The basic resolve action is to put the cursor on the left margin and catch just the right margin of the field and drag it to the right but taking care not to pull the right margin of that field to far least it snap back leaving the user to question what they had done. Being so close to the left margin of Thunderbird made it difficult to discover.
Slackware is very tight about doing updates to a release as they are careful with dependencies, i.e. removing a program I suppose remove a library used by another application that might not occur in the update.
I am trying to take your advice and likewise with rel 4 of Firefox but in that case the app wants to be installed in /opt not in /usr where it occurs originally. My preference is for /opt as that would be the place for a user installed app.