If you are using a high DPI Display with a resolution of 3200x1600 px you can adjust Unity with a System wide Menu and titlebar scaling But Firefox is not really ready for this: All pages and the Icons stay tiny.
multiplication of system font increase and browser font increase makes system controls (combobox, lists, drop down lists) extremely big on many websites, where the form elements are affected by the scaling two times, so all form elements are huge (4x).
emails in Thunderbird are displayed tiny, so you have to use Ctrl++ all the time
How can I adjust Firefox and Thunderbird, so everything will look normal?