after emerge installed mozilla ebuild, it trys unmerge old version. At this stage it remove some files from new instalation (for example, it remove /usr/lib/mozilla/chrome/classic/ recursively). I think these files just moved from distribution and mtime doesn't change
Sorry, I do not understand. If you mean that it removes some directories, sure, but that is because it usually install some empty ones (contents are ir .jar files ...)
Thanks for explanation of this behaviour. I thought emerge delete files, not empty directories. I believe it may be closed.
NP