try restarting in Thunderbird safe mode. Hold the shift key while Thunderbird starts.

I need to make the folder pane wider so that I can read the folder titles.

Try mousing over the right border of the folder pane until your cursor turns into double-headed arrow, then left-click and drag to resize.

TB38.2 Win10

ralphnicholas said

I need to make the folder pane wider so that I can read the folder titles.

On the toolbar > Options

Allow the mouse to hover over the menu and when the sub menu appears select layout and the two folder pane entries