Firefox: Can't delete autocomplete entries

I hope this is the right place to ask, and if not, please direct me to the 
proper group. I did a Google Groups search and found that someone else is 
having the same problem as I am but no resolution was given.

Here's the issue: I'm using Firefox 1.0.6. If I use Shift+Delete to get rid 
of individual autocomplete entries in web forms or the search box, the 
entries disappear for as long as I've got Firefox open. Once I close and 
reopen Firefox, all of those entries reappear. This is a recent issue. It 
definitely used to work properly before. Has anyone here encountered this 
problem or know how to resolve it?

Thanks