Chrome/Firefox: YouTube is filled with all kinds of annoyances, and the YouTube Options extension was our favourite way to fix those for a long while. But now YouTube Options costs $US1.99 a month. If that's outside your price range, YouTube Center does just about everything YouTube Options can do.
YouTube Options was too packed with features to do a side-by-side comparison, but YouTube Center has everything that's really important. You can customise the look, get rid of most elements in the interface, hide comments, disable auto play, change the resolution, and plenty more. You need to install the extension into Chrome manually, but otherwise it works pretty much the same. If that's all a little too much for you, the Magic Actions extension is a bit simpler, but includes most of the popular features of YouTube Options (alongside an obnoxious install screen that asks you to install the developers other extensions).