I’d hate to do any serious work on a smartphone. Writing emails or text messages is as far as I go, apart from that it’s strictly a consumption device (oh, and I sometimes even call people with it).
So no, I don’t see why you’d want to punish yourself editing MusicBrainz on a smartphone or even a tablet. Holiday is a great excuse to kick the habit for a while anyway. 
It seems that I misread the news about Tampermonkey. The author says no versions exist for Windows Mobile (it was earlier, but still).
I have found a Tampermonkey for Android.
I borrowed an Android phone and installed it as well as two of my scripts (ALL LINKS and COLLECTION HIGHLIGHTER).
But, well, it runs in a very minimalist browser, I don’t even know how to go back and all those simple things.
I could not manage to make my scripts run yet, either. Next time I get that phone, I will try again.
On Android, mobile Firefox may also be an option.
Things like http://geo.inge.org.uk/grease-vervet.php seem dead, though.
I have found that Adguard thing, which supposedly has userscripts support, but not sure if userscripts support is part of its mobile versions or not:
I also came across a browser named Dolphin and the Tampermonkey (again?) add‐on for it.
As it’s again something for Android, I cannot test right now.
Wow I’m impressed! 
PINNED SOLUTION!
I could test this with an Android device (model Samsung something) and wow.
Tampermonkey alone at first did not work for mb. COLLECTION HIGHLIGHTER so I thought it was helpless, until I tried mb. FUNKEY ILLUSTRATED RECORDS and wow those thmbnails all showed up before my eyes, I could not believe it!
So, as Tampermonkey’s browser is minimalist crap, I decided to test Dolphin+Tampermonkey as Dolphin looked like a full featured browser.
So I went on and installed mb. ALL LINKS, mb. COLLECTION HIGHLIGHTER and mb. FUNKEY ILLUSTRATED RECORDS, all that.
ALL LINKS worked out pretty well, as you can see, only Wikidata‐to‐Wikipedia doesn’t work (perhaps because of some cross‐domain restrictions that could be lifted up, but no time for further research), I don’t know why:
Know that the background tab is actually loading the collection (41%) in the background, the COLLECTION HIGHLIGHTER script is — like in Opera 12 — not paused when in background! 
Now here is the COLLECTION HIGHLIGHTER loading in foreground:
Here is FUNKEY CAA working on my collection first page:
And here are both FUNKEY CAA and COLLECTION HIGHLIGHTER (once loaded) working at the same time as ALL LINKS (but off screen):
I report this case as a working solution in my first post, which I have turned into a wiki if you want to reference other working solutions yourself, in the future.
[quote=“mfmeulenbelt, post:3, topic:134406”]
I’d hate to do any serious work on a smartphone. [/quote]
Sometimes in holidays I do indeed need to edit when I receive some MB e-mails but my urgent need is to be able to browse artistes and release groups with COLLECTION HIGHLIGHTER on when I am in the record stores (new and used).
I stumbled upon a way of running user scripts on every mobile: bookmarklets, of course!
But the script probably has to be adapted for also running in bookmarklet mode.
And the bookmarklet has to be reloaded on each page you want the script, each time.
So I wonder what script would be good to have in this way…
Thanks to @mmirG mentioning Firefox for Android is able to run all regular add ons, I have tested COLLECTION HIGHLIGHTER with Violentmonkey in Firefox for Android and it worked!
I should soon receive and use my wife’s old Android phone (I have Windows), I cannot wait to be able to test all scripts but most of all to be able to check my highlighted collection on the go, in CD stores!
It is the best 
PINNED SOLUTION so far!
If, like me now, are using Firefox for Android with user scripts and if, like me (because of COLLECTION HIGHLIGHTER), this feature is vital:
Quickly go to Google Play Store to DEACTIVATE FIREFOX AUTO-UPDATE! as version 68.11.0 is the last version that can install Violentmonkey or any other user script extension/add-on, at the moment.
Extension/add-on list for Firefox for Android version 79 does not include Violentmonkey, Greasemonkey, Tampermonkey nor Stylus.
It has been a long time since new Firefox for Android 79+ (Fenix) broke the add-ons.
I was staying in version 68.11.0 (Fennec?) for that purpose, hoping either Firefox would restore add-ons or Vivaldi would eventually support extensions.
Apparently, there are still only 13 allowed add-ons on Firefox for Android, and still no trace of monkeys (Grease/Violent/Tamper).
Hopefully, thanks to a post in Vivaldi extension support request topic, I heard about a Firefox fork with add-ons support: Iceraven Browser!
I was reluctant to install a somehow insecure for me unofficial browser, but it seems now to be the only good solution for Android, I went for it.
I uninstalled Firefox 68.11.0 and installed Iceraven, and it works great for the moment (I only tested COLLECTION HIGHLIGHTER).
As it’s a Firefox fork and as add-ons works great on FF 68, I think everything will be alright.
There is just a Cannot Complete Request small glitch when you install a userscript but don’t worry, the scripts are still installed.
I have had some hindering bugs with userscripts on Iceraven so I’m still staying with Firefox 68.11.0, at the moment.
I am now testing Kiwi browser!
It has been working very good for me on Android 9 with Kiwi browser and Violentmonkey, for 2 months already!!
I just have a problem with user style with Stylus that should be fixed with next version but they are late to upgrade 1.5.22 in the extension store, I don’t know why.
It is the best PINNED SOLUTION so far!
For the record, the problem with Stylus on Kiwi has been fixed, long time ago.
I think there is no more hope with Firefox and Vivaldi extension support on Android.
Both user Violentmonkey scripts and Stylus user styles extensions have been running flawlessly on Kiwi.
Just found out that Firefox on Android does support Tampermonkey again. I don’t know which version exactly, but for me with latest Firefox 112 Tampermonkey is available in the add-ons list for installation, and it works.
Thank very much for this great news!
I have added this option to the original post (anyone can edit the OP, it’s a wiki post).
Strange that they added this closed source add-on before the open source Violentmonkey, tough… 
And is Stylus available, now?
But anyway Firefox was great in v68 but now that I had to switch to Kiwi, it became hard to beat with many more features,like WebDev tools, all extensions, copy link text, print to PDF, etc. 
To use any add-on in Firefox Android currently you’ll need to create a custom collection
Another method to run userscripts on Android in Chromium based browsers is
ChromeXt
inb4 what’s LSPosed/Xposed
Whether it’s worth the risks you’ll need to decide for yourself.
For iOS there are:
Is this new? I use Tampermonkey without the need for custom add-on collection.
Being able to user Tampermonkey is relatively recent.
I didn’t understand why they selected TM but not the others, which are open source.
And can you install Stylus, now?
It was not possible, last time I checked.
The add-on collection is older but is only possible with Firefox Beta.
