Alerts based on tags distribution

Hi, I would like to know if there is an existing methodology to alert/monitor when a specific error has an irregular tags distribution.

If my errors logs a tag named browser. The distribution of visitors to my site is 90% Chrome users and 10% Firefox, I would like to be alerted when a specific error have 50% Firefox users.

Browsers are the obvious example that many developers will manually check themselves, but we have many other tags types that can help us figure out and reproduce sources of problems in our system.

I would like to know:
a. can add the difference vs normal distribution so we could monitor it?
b. whether we can create alerts based on divergence from it.