This browser don't tell all info about text size. Without that, this service can't work properly. We recommend to use Chromium or Google Chrome.
If you're using Mozilla Firefox, you can enable this feature
manually. For this, go to
about:config, find parameter
dom.textMetrics.fontBoundingBox.enabled and set it's value
true. After that, this service will work normally and this
message will disappear. But we can't guarantee that your browser will work
properly. After all, better way is use other browser.