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
In the same Adjust View Properties
window - in the bottom section enable All Folders
the very bottom option - Use these view properties as default
Press 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