Comment 33 for bug 1040313

It looks like you're symlinking folders / files between profiles too: http://bazaar.launchpad.net/~webapps/libunity-webapps/trunk/view/head:/src/webapps-service/unity-webapps-service.c#L827.

This is an accident waiting to happen, and is not really acceptable at all. Firefox prevents multiple processes from accessing the profile folder for good reason, and whilst you might get away with it for the cookies.sqlite (for now), this is likely to cause strange heisenbugs with the extensions folder which could manifest as extensions not loading or being marked as installed by a third party.

(extensions.ini will be replaced by a regular file on the first shutdown after any addons have chaned anyway)

How do you handle synchronization and locking between processes when the addon manager installs addon updates?