What Desktop Environment (and Dolphin) version are you using. Are you fully updated?
Are the hidden files shown when using Dolphin and Konqueror or only when attaching files in FF & TB?
Do you have any add-ons that may cause it?
Again in
View > Adjust View Properties and make sure
Show Hidden Files is
not enabled
In the same
Adjust View Properties window - in the bottom section enable
All Folders And
enable the very bottom option -
Use these view properties as defaultPress Apply > OK
If the above doesn't work you could try creating a new DE user account to see if the same thing occurs.
A quick way of hiding/showing folders is to add the the option to a Dolphin toolbar - mine is like this

The icon named
Hide on the r/h side of the toolbar is the one for quickly enabling/disabling hidden folders (I customised the name to
Hide it's "full" name is
Show Hidden Files (In Dolphin > Settings > Configure Toolbar and in the left hand "Filter" box just enter
hid and it should show it - it's then just a matter of adding it to the
Current Actions side )