F21 has thunderbird-31.6.0-1.fc21.x86_64.
After update to F22 via fedup, there is thunderbird-31.5.0-1.fc22 only.
Yes, the build failed on arm. Jan is looking at it. Thanks for pointing it up.
thunderbird-31.6.0-1.fc22 has been submitted as an update for Fedora 22.
thunderbird-31.6.0-1.fc22 has been pushed to the Fedora 22 stable repository. If problems still persist, please make note of it in this bug report.