Thunderbird Upgrades

We’ve been having some troubles with users who have upgraded from Thunderbird 17 to Thunderbird 24 (despite the jump in numbering, that’s only one version different – Thunderbird recently changed their version numbering scheme to match Firefox). The symptom was that after upgrading, you no longer see any of your email or folders despite the account settings being all present and correct.
We manage our software centrally using wpkg, and as part of that we deploy a prefs.js file which sets a number of default preferences. One preference we set is
pref("toolkit.telemetry.prompted", true)
to disable a prompt which asks if one wants to send usage data back to Mozilla.
It turns out that Thunderbird changed this configuration value from a boolean to an integer, for compatibility with Firefox. This means that if you have an old preferences file with the boolean value, then rather than failing gracefully, Thunderbird 24 becomes totally unusable as described above. You instead need to set
pref("toolkit.telemetry.prompted", 2)
to achieve the old behaviour.
If you’re writing software and need to make a change to the format of your config file: please try to fail gracefully if you receive a config value you weren’t quite expecting!