The read messages in the inbox are not differentiated from the unread messages for any mail server like ymail.com,gmail.com etc. Please check on the problem.

Hi, Please check if this happens in a [https://support.mozilla.org/en-US/kb/Managing-profiles new profile]. If it's okay, you can later [https://support.mozilla.org/en-US/kb/Recovering%20important%20data%20from%20an%20old%20profile?s=profile&r=1&e=sph&as=s copy the personal data] from the old profile. Firefox stores your personal data and settings in another location separate from its files/folder. A new profile would have the default Firefox settings (Tools (Alt + T) > Options and [http://kb.mozillazine.org/About:config about:config] ) and usually would also be empty of any '''Extensions''' and themes ('''Appearance''') in Tools > Add-ons) and their settings. Also, a new profile would have no previous stored history (Tools > Clear Recent History). [https://support.mozilla.org/en-US/kb/Profiles?s=profile&r=2&e=sph&as=s Profiles Howto] [http://kb.mozillazine.org/Profile_folder_-_Firefox Profile Folder & Files] [http://kb.mozillazine.org/Installation_directory Firefox Folder & Files] [http://kb.mozillazine.org/About:config_entries about:config Entries]