We have noticed that Developer Console does some kind of an update on the current user's User record. When that happens, our User trigger is invoked, but with what seems limited permissions, and we get an exception emailed to us from Salesforce saying the following:
"No such column 'FirstName' on entity 'User'. If you are attempting to use a custom field, be sure to append the '__c' after the custom field name. Please reference your WSDL or the describe call for the appropriate names."
The error references a line with the simple query:
List<User> lookup = [select FirstName, LastName, Region__c, UserPreferencesApexPagesDeveloperMode from User where Id =: userId limit 1];
How weird is that? We haven't pinpointed exact action in the developer console that causes this.