cause sometimes it just mess up the webpage.
to make gmail display bigger font, you need to install stylish add on for firefox browser.
https://addons.mozilla.org/en-US/firefox/addon/stylish/
after that, go to this style script --- gmail bigger fonts
http://userstyles.org/styles/438/gmail-bigger-fonts
after install that, you can adjust the font size as you need.
how to adjust font size:
go to firefox add-ons page. select "user styles".
on "gmail- bigger fonts", click "edit".
a window will popup.
you want to look at line 7, "font-size: 14px !important;"
change the number before "px" to 15 or 16.
don't forget to click "save".
