The F28 change to use the SQL DB storage by default for NSS might cause users on slow filesystems to experience slow performance with some applications, such as Firefox.
The workaround for those users is to explicitly set the environment variable NSS_SDB_USE_CACHE=yes.
Although we cannot automatically detect all scenarios where this environment variable should be used, and setting it for everyone would cause performance regression for most, it would be good to implement an enhancement, that helps most affected users.
A reasonable strategy is to check the filesystem type, and enable caching for known slow filesystem types, and do probing for types of questionable speed. This is a best effort attempt.
Code is currently being worked on in upstream bug
but it might take until NSS 3.38 end of June 2018 until this code gets released.
I suggest that we take the upstream work as a downstream patch for Fedora 28, until it gets released upstream.
The current F28 package contains the fix, so closing this.