I'm not sure what it is you think you'd be automating -- or even quite what it is you are doing that would be "cumbersome" or "time consuming" unless you're wasting time on scripttardery that has ZERO business on a WEBSITE in the first place... and it at least sounds like you're talking about websites since you're talking different browser engines.
But the core of any new features or scripting is features detection, which in most cases shouldn't be anything more than a single line "if" statement unless you're going to polyfill or implement a fallback.
What you don't want is to start "browser sniffing" unless there's really no other way, and by "no other way" I mean legacy IE.
Though your picture has one of the poster-children for things that just piss users off and therein has zero damned business on websites: push notifications that cascade to the OS. SCREW THAT! Number one thing I have people asking me how to disable when some jackass website tricks them into accepting them.
Bottom line though, if you're developing a WEBSITE your job is to deliver content to users in as accessible a manner as possible. That means semantic markup, separation of presentation from content, progressive enhancement so that it gracefully degrades... and to that end as the old saying goes:
If you cannot make a fully functional website without JavaScript FIRST, you likely have zero damned business adding scripting to it!
That's not some cutesy catchphrase, remember you don't work scripting off, you're not meeting WCAG minimums and as such depending on the type of website and industry could land yourself in COURT. Or end up with a money pit the client pays to settle dozens of cases a year rather than fix YOUR stupidity.
Which is why so much of the new "gee ain't it neat" scripted nonsense is just more of the industry flipping the bird at the REAL reason websites exist -- delivering content to users. Same as the asshattery of dicking around drawing PSD's and calling it "design", screwing around with bloated frameworks that undo twenty years of progress, or any of the dozens of other middle-fingers to usability, accessibility, and sustainability that haven't just been hot and trendy the past decade, but have become the 'societal norm'.
But you know what Ron White said; you can't fix stupid.