I still have it in nightly:

Three dot menu -> more -> Add app to homescreen
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I still have it in nightly:

Three dot menu -> more -> Add app to homescreen
Well it's good to know it hasn't been removed, but I don't have that. Did you install from the Play store or from F-Droid, or somewhere else?
Play store. Ill try fdroid.
Edit: https://www.reddit.com/r/firefox/comments/u7qgu6/why_arent_official_firefox_apps_on_fdroid/ <- this might be your problem?
Edit2: or not, fennec also has the button :/ no idea why you dont see it.
Is this a beta version? I have the latest FF mobile but my interface looks different than this...
I wonder if it's some kind of A/B test or something. Or they got too much negative feedback and rolled it back. I saw this UI for like a week or two on my previous phone but when I got a new device and installed FF it was back to the old UI. Not on beta or nightly channels or anything, just standard releases from Play Store.
I was wondering the same
Here's my build info:
146.0.1 (Build #2016132551), 86bb7f6af6312ba3c0161085f854bcdff68f1a91
GV: 146.0.1-20251217121356
AS: 146.0.2
OS: Android 15
Weird I have the same version.
They redesigned the menu a while back, afaik it's been rolled out in the main release already. But perhaps they have a gradual rollout to gauge bugs and feedback.
I have it on the latest version, both for websites that provide a web app instance ("install"/"add app to homescreen"?) or for generic web pages ("add website to hs").
The permissions you are looking at in the ss are the "dangerous" android permissions, and usually "add links to the homescreen" is not there. On my xiaomi to grant it (if it isnt by default) you long press the app to go into the app info, then something like "other permissions" or "special permissions".
Weirdly, I do have a "special permissions" section in my phone (Fairphone 4, which basically runs stock Android 15), but there's nothing about adding links to the homescreen in there, just:
I actually went through all of these, enabling Firefox's permissions wherever it came up, but still nothing. I'm starting to think that this might be an Android (b)locking rather than a Firefox shortcoming.
It's gone for me too on my firefox on ios 26 with an iphone se2.
Does it appear on other websites that do not provide an app?
It doesn't appear on any site. Note that I'm not looking for an "Open with the app" button, but rather one that creates an "app" that just opens Firefox at a particular URL. This used to exist, but doesn't seem to happen for me anymore.
HTTP Shortcuts on F-Droid does it better with better control IMO. This is what I use now.
Not quite what OP is asking for, seeing as they just want to open the site in their browser from the home screen.
But anyway, it's funny how that app has somewhat advanced scripting features a-la Tasker, but built strictly around firing http requests.
It does open websites in their browser from the home screen. I wouldn't have recommended it if it didn't do that.
You can even get it to open in a specific browser instead of the default browser.