Browser based apps cheat sheet

I’m looking for a cheat sheet of sorts for people new to browser apps. Let me build a little bit of context first.
I have a lot of experience testing things that are not browser based, mostly native apps, API based systems and even use appium and selenium to drive mobile apps. But of late I’m roped in to test an inward facing web based suite. I’m trying to start with a clean slate and not rely on the existing tester to show me all the old bugs, which are rather pointless. We already have a lot of selenium tests, and we will be extending these substantially I imagine, but as a team. For example I’m going with Page-Object-Model to speed up and make new E2E test flows easier to build robustly. It’s a huge suite of “internal” apps, and my lack of experience in the browser means simple things like browser cache bugs (which we all find accidentally but never by intent) and bugs I don’t know about in web apps are giving me a bit of a sleepless night. I have minimal JavaScript smarts, and I’m looking particularly for gotchas and simple tools like for detecting if your app is using too much memory in a tab? What should happen if I zoom CTRL-minus out like crazy far? What kinds of browser plugins can break my app unexpectedly? What common browser is a pain to test on, and what perfectly normal browser options will cause apps to degrade badly (like disabling hardware acceleration)? All that kind of thing.

My goal is to spec a load of areas to explore off the beaten path of simple things like logging into the app, clicking about and logging out again, that’s not going to find many high value bugs. I’ve got some runway available to me due to a number of pieces of the site being rewritten in totally different ways, hence want to be the fresh eyes, but get some good tips from the best community on the planet.