My preferred way to get userscripts on Android would now be to use the Firefox browser, which has working, well-maintained Add-ons available for both Greasemonkey and Tampermonkey (search for them through the Add-ons menu in the Firefox app).
You can add (and execute) bookmarklets entirely in Android Chrome.
The caveat: it takes more work than just drag-and-drop in the desktop counterpart.
Save a bookmarklet (Android Chrome)
Long tap the desired bookmarklet
Select Copy link address
Go to Menu (three dots) and tap the Star (bookmark)
BEFORE IT DISAPPEARS, tap EDIT! (at the bottom)
Bad news it seems. Bug report on Google code
The most relevant post is this:
Yes. It is as design. "autoplay" is disabled for Chrome for Android
It seems that Android 4+ changed the requirements for the play() method to require user interaction.
Article on this issue
It's worth nothing that many comments refer to getting it to work with a hack/...
This can be turned on/off in Chrome using flags. This is on the user end though and cannot be change in the browser from a website or app.
You can also do this in your own app using the api for webview or websettings and make "getMediaPlaybackRequiresUserGesture(false)" it is by default set to "(true)"
My guess on why V8 on PC is much faster than V8 on Android is ...
There is a Greasemonkey-like add-on for Dolphin called Tampermonkey. There is also a stand-alone Tampermonkey app, but Dolphin is a more full-fledged browser than that thing.
There is also a similar add-on for Firefox for Android, called USI.
Use either the Habit Browser or Slepnir Browser apps. They both support Userscripts. I had to tweak my scripts slightly to get them working (they handle events differently) but they both work really well.
Works in Chrome mobile. Here's the recipe:
Create a bookmarklet = add a script to your bookmarks:
on Chrome PC¹, then sync (so your bookmarks show up in Chrome mobile on your phone)
or directly in Chrome mobile on your phone²
Do not invoke/call the script (on phone) by looking it up in Chrome Bookmarks (menu [ ⋮ ] / Bookmarks) → that doesn't ...
Just go to Settings of Google Chrome Browser (Open Google Chrome Browser and click ...
HTML5 ServiceWorker seems to support what you need via BackgroundSync / PeriodicSync feature. However, since ServiceWorker is still an ongoing effort, I'm not sure what features are currently implemented in Chrome. I couldn't find any good demoes of this, only proposals: https://github.com/clelland/BackgroundSync/blob/master/explainer.md
Cordova has ...
As I mentioned in the comments the Twitter app doesn't seen to have an in-app browser so I'm using the Reddit Is Fun app instead since I know it does. I think that all in-app browsing uses a WebView so it should be the same across all apps. The WebView and Chrome both use the WebKit engine but Chrome seems to use a more up-to-date one. I tried out SunSpider ...
It turns out my probably was solved by something as simple as clearing my cache.
Which makes me feel pretty stupid, because I should have done that before even bothering to ask. I never suspected this could happen straight out of the box, guess I was wrong.