Bug reports and feature requests related to the MediaWiki software which powers Wikimedia projects should be filed to Wikimedia's bugzilla. Bugzilla is a bug reporting tool and organization system used by many software projects.
For emergency problems on Wikipedia & sister projects, try to contact the developers by IRC (#wikimedia-tech on irc.freenode.net) or on the wikitech-l mailing list (please subscribe to ensure that your message gets through and you receive replies).
Useful queries 
Lists of currently opened bugs (including feature requests):
- Wikimedia (Configuration issues and other issues specific to Wikimedia servers, Wikimedia websites (including Wikipedia, Wiktionary, Commons, and the MediaZilla bugtracker) and other Wikimedia specific things)
- MediaWiki (The wiki software itself -- most issues about how the wiki works should go here)
- MediaWiki extensions (MediaWiki extensions, including EasyTimeline, CharInsert, Renameuser, Cite, etc.)
Feature requests are called "enhancements" in Bugzilla jargon:
Search by votes:
Reminders for users 
If you find yourself dissatisfied with the level of service you are receiving from developers, please take note of the following facts:
- Most developers are not paid.
- There are hundreds of unfulfilled feature requests, an ever growing number.
- There are hundreds of thousands of users and only a small number of developers.
- Developers don't work 24 hours a day, plus there are different timezones on this world.
- Everyone wants to help, but no one has any obligation to fix all the bugs that you want fixed, or to answer all questions.