We've split the oudated browser detection script into two parts: 1) the detection if the browser is outdated and 2) the showing of the message to users with outdated browser.
The detection part is what you embed into your site (update.js). This is what all users will have to download. And this is is now only 2.2 kB in size gzipped, five times smaller than before
(>10kB).
Then, if the browser is outdated and needs to be notified, the message file (update.show.js) will be loaded, but this will only happen for about 1% of the users.