Thank you for your question.
The font used for the title bar in Internet Explorer (the most common
browser)or any Windows application for that matter, is selectable by
Right click a blank area on your desktop and then choose properties.
Go to the Appearance Tab.
Now, you can either left click on the Active Title Bar (with the
colored gradient as you note) or scroll down the item drop down list
to "Active Title Bar".
Below that is a drop down list that will show the font currently used
for this Tile Bar. In my case, I am using Microsoft Sans Serif in
white, size 10. You can select other choices that might appear better
or more pleasing for you depending on the resolution of your monitor
(800x600, 768x1024, etc.) and what you prefer to see.
You can also change the Inactive Window title bar font as well as many
other settings from this appearance tab. And then you can save them as
a scheme by naming it and saving. As a matter fo fact, you might wish
to save your current settings as a scheme before you make changes so
you can always revert to what you have now if you find you don't like
the changes you make.
Personal knowledge of Windows
I trust my research has provided you with the answer you desired. If a
link above should fail to work or anything require further explanation
or research, please do post a Request for Clarification prior to
rating the answer and closing the question and I will be pleased to