macOS bugs causing sporadic browsing issues with Safari, Firefox, others
An apparent bug -- or series of bugs -- in macOS 11.3 and 11.3.1 is causing seemingly random website browsing problems in Apple's Safari 14.1, as well as on other browsers.

Credit: Apple
According to user reports on the Apple Support Communities, the Safari 14.1 update breaks functionality on popular websites like eBay. The issue appears to predominantly affect Safari 14.1 on macOS Catalina and macOS Mojave.
There are reports from developers about ongoing problems with the latest versions of Apple's browser, too. Google Chrome developer advocate Jake Archibald reports that localStorage in Safari 14.1 is broken, causing tabs with use the same localStorage for text boxes.
Other reports indicate that Safari 14.1 for macOS Mojave and macOS Catalina also has problems with WebAuthN. According to Eclectic Light, Apple pulled the Safari 14.1 update for both of those macOS versions on May 1.
AppleInsider staff members have also run into website problems with macOS Big Sur and Safari 14.1. Problems across our staff don't stop at those browsers, since we've also noticed website functionality issues in Firefox and Google Chrome on sites like eBay and others.
As far as potential fixes, there doesn't appear to be anything surefire. Some users report that disabling JavaScript in Safari preferences seems to resolve some of the issues. The troubleshooting advice given by other users in the Apple Support Forums suggest that a clean reinstall of the operating system solves the problem, but AppleInsider can confirm that this is not a universal solution.
In the meantime, it appears that Apple is aware of the problems and is likely working on a fix, as evidenced by the removal of Safari 14.1 for macOS Mojave and macOS Catalina.

Credit: Apple
According to user reports on the Apple Support Communities, the Safari 14.1 update breaks functionality on popular websites like eBay. The issue appears to predominantly affect Safari 14.1 on macOS Catalina and macOS Mojave.
There are reports from developers about ongoing problems with the latest versions of Apple's browser, too. Google Chrome developer advocate Jake Archibald reports that localStorage in Safari 14.1 is broken, causing tabs with use the same localStorage for text boxes.
localStorage is broken in Safari 14.1.
Tabs end up with seperate localStorage for reading, but the same localStorage for writing. This will likely result in data loss for users. (h/t @forresto)https://t.co/5Ljxl4vvbH-- Jake Archibald (@jaffathecake)
Other reports indicate that Safari 14.1 for macOS Mojave and macOS Catalina also has problems with WebAuthN. According to Eclectic Light, Apple pulled the Safari 14.1 update for both of those macOS versions on May 1.
AppleInsider staff members have also run into website problems with macOS Big Sur and Safari 14.1. Problems across our staff don't stop at those browsers, since we've also noticed website functionality issues in Firefox and Google Chrome on sites like eBay and others.
As far as potential fixes, there doesn't appear to be anything surefire. Some users report that disabling JavaScript in Safari preferences seems to resolve some of the issues. The troubleshooting advice given by other users in the Apple Support Forums suggest that a clean reinstall of the operating system solves the problem, but AppleInsider can confirm that this is not a universal solution.
In the meantime, it appears that Apple is aware of the problems and is likely working on a fix, as evidenced by the removal of Safari 14.1 for macOS Mojave and macOS Catalina.
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http://swcdn.apple.com/content/downloads/36/06/071-02600-A_V0GH526IV1/1cn8scgv7ujlqsglord2zkdyy3ho2ebunz/Safari14.1MojaveAuto.pkg
It's been error-free. There's also a direct download for Catalina here:
http://swcdn.apple.com/content/downloads/62/62/071-00728-A_5SWQUDK0WB/jyq47oimzangibo4lmyevte0ezlrg8w8s9/Safari14.1CatalinaAuto.pkg
It seems that the built-in software update did not update all of Safari's support packages, in particular libwebrtc.dylib at /System/Library/StagedFrameworks/Safari/ was out of date (should have a created date of 22/04/2021 for Mojave)
I found out this week a family member's entire family has switched back to W10 (PC's) and are happier so far... I'm holding out on moving on from High Sierra because everything (mostly) 'just works' (and I can get work done) vs 'upgrade' turmoil, costs and workflow reinvention of questionable benefit...
Has the cost in time, frustration and lost productivity of annual macOS 'upgrades' since 2011 become an increasingly unreasonable burden in a seeming attempt to 'monetize' (or sunset) everything Apple ? Would returning to a pre 2011 2~3 year macOS development cycle be more beneficial and merit based for customers (vs developers?) than attempting to drive increasingly non-upgradable hardware sales and iCloud data collection creep with rapid planned obsolescence cycles...?
By way of example Snow Leopard was supported for roughly 6 years from 2008 through 2014, and Rosetta effectively offered application support for both OSX and Classic (System 9, Y2K) for roughly 9 years through 2009.. Did that help define 'Insanely Great'...?
https://en.wikipedia.org/wiki/MacOS#Release_history
https://en.wikipedia.org/wiki/Classic_Mac_OS#Transition_to_Mac_OS_X
I’m equally invested in both Apple and Microsoft and see that each operating system has its pros and cons. They are much more alike than they are different and both of them have plenty of latent software issues and updates sometimes don’t go well. Just last week I had to do a reinstall of Windows 10 on a machine that was borked by a Windows Update. But I also had serious issues with two Macs upgrading from Big Sur 11.2.x to 11.3. Apple messed up something in the Desktop & Screen Saver feature when it’s pointed to your Photos collection.
Microsoft does support a much wider hardware base and you can install Windows 10 on some seriously ancient hardware, but what you can do versus what you should do is widely divergent. As an experiment in what “is possible” with Windows 10, I installed in on an old Samsung netbook with 2 GB RAM and Atom chip. It installed just fine, with a lot of patience required. It boots and runs but I wouldn’t subject anyone I actually like to having to use this computer to try to get anything useful done. Even Notepad struggles to keep up with slow typing. On the other hand, a base level Debian Linux (32-bit) on the same hardware is actually reasonably functional for basic computer tasks, like word processing, browsing the web, email, etc.
Glad to hear your family members are happy with Windows 10.