I haven't done a lot of userscript dev, but based on my experience so far, all of this advice is spot-on. I found it useful to create a `waitForElement(query)`

I haven't done a lot of userscript dev, but based on my experience so far, all of this advice is spot-on. I found it useful to create a `waitForElement(query)` helper function that takes a CSS selector path and returns a Promise that resolves when the query starts finding a match in the DOM. (Internally, it's just populating a table that is iterated over in the MutationObserver callback.) As for SPA "navigation", I had trouble with popstate events. I hadn't considered your <title> trick; I'll bet that would have worked for me! Right now, I'm polling window.location.href every half second, which sucks.