Following the rather acute divergence in opinion regarding the ideal length of characters for a tweet, one extension offers you the ability to shrink longer tweets back down to 140 characters.
140 character limit RSS
Twitter recently started testing an increased limit of 280 characters per tweet for select users. If you weren't one of the lucky few, you can activate the feature by following this tutorial.
Twitter has announced it will now no longer count username @mentions in replies towards the 140-character limit. The feature is currently rolling out to the website and the iOS and Android apps.