Sometimes you might want to compare both sides by file size only, ignoring last modification timestamps.
Instructions:
Open file "GlobalSettings.xml" located either in "%appdata%\FreeFileSync" or the installation folder and change the value of XML node <FileTimeTolerance> to some sufficiently large number of seconds, for example 2.000.000.000. Changed files will now be detected as a conflict (same date, different file size) and the default synchronization direction for conflicts can be used.