Then how are we to fix it? You can set the font size used by most applications in the windows control panel.
Select Display, then Appearance. In Appearance you can set the font size that most applications will use.
In your browser, you can enlarge, and set the smallest size websites display. Go to Tools, click options, and then the content tab. There you can set the default font sizes for rendering websites.
Otherwise, what does this have to do with Zbrush?
It’s not pixologic’s fault if the font is too small to read in Photoshop… 
So Ctrl and + for web browser