After manually pruning the external Lightning extension from profile (see #553266 ) and removing extensions.sqlite the built-in Lightning extension is shown in addons. It is shown as disabled, and none of the buttons associated with it (Preferences, Enable, Disable, Remove, ...) do anything. So it can't be installed, used, or removed. For great justice!
The "built-in" lightning extension is actually a misnomer in 38.0.1 -- it's not built in but rather bundled, and installed into the user's profile and run from there. thunderbird-38.1.0 restores the USE="lightning" flag, which installs the calendar and gdata-provider app-global, rather than it being copied into profiles based on some unknown heuristic -- essentially putting it back to the way it was for thunderbird-31.x[+lightning]. There isn't a way at this time to completely disable lightning installation, other than to turn off the use flag and add {/usr/lib*,/opt}"/thunderbird/distribution/extensions/{e2fda1a4-762b-4020-b5ad-a41df1933103}" to INSTALL_MASK. Let me know if this improves the situation at all.
In 38.1 the preferences work as expected.
Good, so this one can be RESO/FIXED then? BTW, is this with USE="lightning" enabled or disabled?
If you feel I have closed your bug and it is still a current issue, please reopen and update it completely. We will not work bugs that have no ebuild in tree any longer or can not be reproduced with a current system. Thank You for your support and understanding The Mozilla Team
