Then I found out that you can use the same WebKit parameters you use in Safari to change some of NetNewWire preferences. Just type this in your favorite console (Terminal or other), then press Return:
defaults write com.ranchero.netnewswire WebKitMinimumFontSize 13
I also attempted to kill GIF animations, but unfortunately, setting these parameters to 0 didn't work:
WebKitAllowAnimatedImagesPreferenceKey
WebKitAllowAnimatedImageLoopingPreferenceKey
You can use PithHelmet to stop animations, but the SIMBL (the framework that is required to run PithHelmet) caused some glitches with Gmail, so I stopped using it.

