Changing font size
Is there any way to change the font size on this forum?
You'd need to change the CSS file for that. But that's a file on the server and not a user setting.
There are posts which have done this before. All are by administrative level users.

A couple of days ago, I could change text size in the subject line...
If someone wrote an user script it could affect the look or functionality of the DN.
You can also use ctrl-minus to make text smaller, though that downsizes everything else in modern browsers too.
You can also use ctrl-minus to make text smaller, though that downsizes everything else in modern browsers too.