Is it possible to merge email@example.com into firstname.lastname@example.org?
No, bugzilla doesn't have any merge functionality, so we can't do that.
Gnome's bugzilla has merge functionality.
What version of buzilla does freedesktop use?
We use 5.0.4. GNOME have significant changes and customisations to their version of Bugzilla, whereas we run mainline. The user-merging functionality is not supported by upstream and might do damage. Frankly we don't have the time to support this. Sorry.