Have you tried enabling 'pixel rounding' in project properties? (new to r59)
If you set an object's position between two pixels (e.g. X = 2.5), most browsers display it with linear filtering, to make it actually look like it's half way between two pixels. However, for fine pixel art, that can make it look blurry. Pixel rounding always forces the draw position to be rounded to an integer which should fix the problem.
Setting an object between pixels is more common than you might think: all the behaviors do it. For a lot of games, it makes the motion look really nice and smooth, but it doesn't suit pixel games.