On each update/unmerge of www-client/mozilla-firefox, the directory /usr/lib/nsbrowser/plugins is deleted with all its content.
The firefox ebuild itself has no files in this directory, but other ebuilds providing plugins. Those plugins are missing after update, causing reinstall of the providing packages.
Steps to Reproduce:
1. install mozilla-firefox and a plugin-providing package (e.g. mplayerplug-in)
2. update or unmerge and reinstall mozilla-firefox
3. try to watch an video with firefox (e.g. mpg)
Firefox opens the dialog, asking where to save or how to open the media
It should find and use the previously installed plugins associated with the media-type in /usr/lib/nsbrowser/plugins
As noted in the ebuild, this is intended. Leaving the stuff there breaks install.
elog "Please remember to rebuild any packages that you have built"
elog "against Firefox.