If you find it make a couple of copies in another folder. Then:
-open Firefox
-open the Bookmarks menu
-select Manage Bookmarks
from the window that appears:
-open the file menu
-select Import...
From the window that appears:
-select From File and click next
-browse to location you saved the file
-select the bookmarks.html file and click Open
If that doesn't work try it again using the bookmarks.bak.
Sounds like the hard drive may be failing or corrupted. I suggest you do a full backup of the important stuff.
Did you find any words of wisdom on the firefox web site support forums?


