Inability to attach Dropbox files from attached and mapped drives

My files are stored on external hard drives within Dropbox. The hard drives are mapped to my computer. I can no longer attach files from these drives to anything through Firefox. I can still attach through Chrome, Bing, Safari etc. Any suggestions how to solve this problem. I am NOT attaching through the Dropbox website. I am attaching through the full path showing drive etc. Thank you.