Comment 7 for bug 338251

Until the patch hits, according to the upstream bug, it looks like this feature was mis-implemented to mean the exact opposite of what it meant in the past. In other words, any characters you put in that box will be used to _break_ words apart, rather than join them.

With that in mind, you can still make it work the way you want. I put in:

"';

To break words on quotes and semicolons.