"Browse button" suddenly stops working

This issue is quite complicated, I will try to give a maximum of details. -- Environment details We are in a Windows 2012R2 corporate environment, with Windows XP/7 workstations. In order to standardize our users environment, their Firefox and Thunderbird profiles are stored on a network share, like this : \\server\userprofiles\username\firefox.profil We use Active Directory folder redirection for Application Data, so %APPDATA% is stored in the following folder : \\server\userprofiles\username\Application data Naturally, Firefox's profiles.ini is stored in : \\server\userprofiles\username\Application data\Mozilla\Firefox We customize this file in order to use a relative path. Here is the content of our profiles.ini file : --------------------------------------- [General] StartWithLastProfile=1 [Profile0] Name=default IsRelative=1 Path=../../../firefox.profil --------------------------------------- We don't use an absolute path because we don't want to manually edit the profiles.ini of each user to set the correct path ( Path=\\server\userprofiles\username\firefox.profil) These settings works correctly. -- Problem Sometimes, users complaint about "Browse button" (input type="file") not working anymore. Actually, when we look further : * The "Browse button" is really not responding (nothing happens when we click) * However, we can drag/drop a file on the input area, the file is accepted and can be uploaded * It seems that something is locked, because when we go to "Bookmarks" the dialog box is empty, we can not add or import bookmarks * Restarting Firefox does not help * Closing Firefox, deleting the remaining parent.lock file does corrects the issue Are we doing something wrong ? Do you think that using a relative path with "..\..\.." is a bad idea ? Thanks