So, I had to fix that in order to continue reading the documentation.
In the page source I identified the line:
<link rel="stylesheet" href="//fonts.googleapis.com/css?family= Roboto:regular,medium,thin,italic,mediumitalic,bold" title="roboto">
It's basically this Roboto font that makes me sick.
The easiest solution was to block fonts.googleapis.com at the system level, i.e. add
127.0.0.1 fonts.googleapis.comto C:\Windows\System32\drivers\etc\hosts file. That did work, the browser replaced missing Roboto with the default Arial (which is perfect). But I didn't want to totally disable Google Fonts API (in case if some webside uses it for actually cool looking font).
Since I am using Firefox, I checked if there are addons that can filter HTTP requests using resular expressions or wildcards. Redirector addon didn't work: it seems to redirect only URLs you enter in the address bar.
And finally BlockSite addon was just what I needed. I added the following URL to the black list:
... and enjoyed reading Arial.
Still, it is very annoying when Google adds new "looks" and "features" without giving users an opportunity to say they hate it!
PS: I switched back from Chrome to Firefox for a similar reason...