For firefox, just stick with UBO. Should be sufficient.
Yup, keep it simple to minimize tech support calls.
Use Ublock Origin and be sure to select better filters, get her using Bitwarden the password manager, and use Quad9 DNS to block lots of bad websites and malware.
O&O Shutup is a nice Windows software to block lots of crap.
Yep, bitwarden would help for phishing so she isn't typing in passwords in different places. If you can, you can also get the fingerprint set up so it's easy for her to scan. You can also get external ones for desktop, but I'm not sure how good the sensors are so YMMV
At 77, she should just use whatever she's comfortable with. So I wouldn't switch her email or anything like that, because you'll be on the hook if anything goes "wrong" (i.e. she'll blame the changes if anything surprising happens, even if it's her fault).
If you can, get her to use email less and other forms of communication more to help prevent phishing scams and whatnot from impacting her.
I second this.
Had to fix up mum's laptop and she wanted Windows 10 with all the Microsoft Office gubbins (she had to settle for Libreoffice). Didn't want a word of anything Linux because "it might not work with any of my stuff". I don't know of a single thing she does outside of web browsing and typing up word documents.
You just can't change some people.
And the goal shouldn't be to force someone to change, but to convince them that changing is in their interest.
Maybe have her try your computer (set it up with something familiar like KDE) and see how she likes it. Have her try the web version of Office. If there's an app she uses a lot, have her try an alternative. If she really doesn't like it, install Windows, make it as clean as you can, and try to get her to change one app at a time.
At the end of the day, it's her computer and you're just setting it up for her. If she understands why you think something else may be better for her, maybe she'll give it a solid shot.
Would she notice if you gave her a Linux machine but with a Windows 10 bootsplash?
Probably, she uses Windows 10 at work.
Besides ublock origin like the other posted stated your biggest scam threats would be coming from social media websites, Facebook or meta whatever its called and email being the biggest. Since I assume you can't monitor her 24/7 and she's an active user, setting up some kind of DNS solution and firewall on your network, you managing her passwords and 2fa via hardware, setting up a non admin local account for windows and maybe some kind of easy reference material like pictures with text in a booklet should be used also. Assuming she's still sound of mind
Edit: as for the phone portion of the question it really depends on how much media do you want her exposed to? You can make a pretty dumb phone via grapheneos and install the games she plays normally (network access restricted of course) with automatic updates. But if she uses social media, messaging apps and other apps like that maybe an iPhone would be easier and simpler for her. At that point you will have to rely on your network solutions, you managing her account credentials, bank included, and the reference material to protect her from scams
I install Fedora Kinoite for grandma's and think its great for them.
That looks interesting. I'll put it on her old laptop and see how it looks.
Mx linux is another try if you want more flexibility installing programs and tinkering with it
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