Haven't tried it, just the first result on Google: https://thp.io/2008/urlwatch/
Diffs are easy. You could do this in a couple dozen lines of bash. There are many modules and libraries for parsing XML/HTML that would offer more advanced functionality. Would probably take me a half hour to make a Python script that watches a particular part of a web page to avoid ads, comments, etc. causing diffs.
I achieve this by setting a cronjob in Linux with specific URLs to watch, using the urlwatch software: https://thp.io/2008/urlwatch/ If you're very careful about the URLs you choose, it can become an accurate method of notification. I imagine there are a number of software packages or even web-based services available that will provide similar results.
Have you considered using urlwatch as a non-browser-dependent way to check for changes? It has a regex search/replace feature which, although regexes aren't ideal for working with HTML, I've found handy for excluding parts of a page I don't care about changes in.
Because it's a contract, and if I agree to it it's binding, so I want to make sure I'm not giving away my house or whatever.
I tend to find a good rule of thumb is to search (Ctrl+F) for "change" or "update" and see what the clause is that deals with changes to the terms. If those are reasonable, like "if we change the terms we will inform you with at least 30 days notice before the changes take effect", then its likely the rest of the terms are pretty reasonable, and I feel fairly safe skim-reading the rest just so that I did.
On the other hand, if they're unreasonable, like "we reserve the right to change the terms at any time, without notifying you, and you agree in advance to be bound by whatever changes we make", then I either a) nope out of there immediately, or b) spend a bit more time evaluating whether I really want to use whatever service it is, and then read the terms carefully, and then set up urlwatch on the t&c page(s) to let me know when they do change.
While I see the benefit of having this information exposed over a webpage, I'd be weary of running any webserver on a baking node. The recommendation is to not even open port 9732.
I run this script via urlwatch and get a telegram alert if the status changes. Despite being described as "a tool for monitoring webpages for updates", it monitors changes on webpages and any script output.