Abrowser's default sans-serif font

I usually just manually change the sans-serif font to Arimo, the serif font to Tinos, and the monospace to Cousine.

Btw, if you don't have it installed on Trisquel 7, you should install fonts-croscore which has Arimo, Tinos, and Cousine which is equivalent to the popular Arial, Times, and monospace fonts some sites may be hardcoding for Windows users. These are basically the improved versions of the Liberation fonts.

If you need a Calibri equivalent, there is fonts-crosextra-carlito and if you need Cambria, there is fonts-crosextra-caladea. You can read more about these at http://packages.trisquel.info/belenos/fonts-croscore.

I had the same question some time ago. I don't know if still the same, but it used to be "droid sans".

While we are talking about default fonts, here is the default sans-serif one I use: https://www.google.com/get/noto/

It's a free font set, licensed under Apache 2.0.