well, I wanted to make sure that your post doesn't end up with no responses (0 replies | 8 views).
I am not sure If I will have an answer for you but as it seems like this is pretty tough to resolve.
How about you just use another webbrowser such as Galeon.
I typically have to do CTRL + 8 sometimes which increases the font size by 10% I believe. However, whenever I want to reset it back a CTRL + 9 zooms it back into a 100% view.
You should give Galeon a try...as far as I've heard it's one of the best browsers (GNOME) and I personally can't complain!
Hope this helps!