Firefox has taken over my Directory Tree!

[WasserLand]

Ubuntu 10.04.

I go to Places>Home and the directory opens in Firefox.  It presents as
a page and is headed: "Index of file:///home/. . . ." etc.  I can't open
files or do anything with them.  a right click presents a dialogue box
offering to "copy link" and other link alternatives.

I've hunted high and low for the inevitable tick that I can un-tick to
get things back to normal.

Does someone have the solution, please

Dave W