Weird font kerning issue on Chrome and Firefox

To expand on Gunnar's answer, I was able to ameliorate the font kerning issue by commenting out the following passage in 56-kubuntu-noto-conf:

  <!-- Roboto is BCI-hinted for widely used LGC characters -->
  <match target="font">
    <test name="family"><string>Roboto</string></test>
    <edit name="hinting" mode="assign"><bool>true</bool></edit>
    <edit name="autohint" mode="assign"><bool>false</bool></edit>
    <edit name="hintstyle" mode="assign"><const>hintfull</const></edit>
    <edit name="antialias" mode="assign"><bool>true</bool></edit>
  </match>

Still have no clue why this is necessary - in my case I just migrated to 20.04 from 18.04 where this issue was not present. The workaround above seems to work fine for now, however.

The default font in Kubuntu is Noto Sans. As an experiment you may want to disable the Noto configuration and with that fall back to DejaVu Sans:

cd /etc/fonts/conf.avail
sudo mv 56-kubuntu-noto.conf 56-kubuntu-noto.conf.disabled