Ran into a strange issue where uploading files through Firefox would cause the whole system to freeze.
Firefox - 97.0.1 (64-bit)
Zorin - 16 / 64-bit / X11
Fix - in Firefox - Settings - Privacy & Security - Cookies and Site Data
Clear "Cookies and Site Data" & "Cached Web Content"
This is annoying as you'll have to log into websites again but this is the only fix I found that worked. There wasn't a lot of information on this issue so hopefully, this might save people time in the future.
What happens if you try another browser, such as Falkon? You also mention upload problems - not Box is it? I had been using Box for when I created the unofficial manual for Zorin 12. Then they changed their modus operandi and downloaders had to sign up for a Box account before they could download the manual. I contacted them and they told me:
I'm curious how Firefox is installed. Did you remove it and reinstall? I'm also curious how much ram and what type of processor you have. Gnome can take a lot of ram. Increasing the swap file size may be beneficial, but i couldn't say without knowing more of your system.
Hi, I tried other browsers and they worked fine, seems to be isolated to Firefox at this time. Thank you for your reply.
Hi, I installed the browser from the software store on Zorin.
Hardware specs:
Intel® Core™ i7-1065G7 CPU @ 1.30GHz × 8
16 GB RAM
1TB HD with 300GB Windows / The rest for Zorin. Windows was installed first.
I do seem to have a swap file.
Swap isn't going to matter because you will never use 16gb of ram. It's a newer system, try snap list and flatpak list in the terminal looking for Firefox. If it comes up in either list, remove it by the software store and go back to the terminal. Type sudo apt install Firefox. This will install the apt version, less problems because of double sandboxing.
If it isn't a snap or flatpak, is check how many extensions you are running and whether you have hardware excelleration enabled (because of your specs it may have already opted for this, maybe not). If all this still results in freezes, uninstall and reinstall Firefox.
Don't try to install multiple versions of Firefox simultaneously. If one version exists, remove it before trying another version. It will cause conflicts if you don't.
I've installed the apt version and done a bunch of testing, seems stable and haven't had any issues. Thank you for your help. 
I'm glad to hear that this has been resolved. After some testing and ensuring that Firefox doesn't freeze again, would you mind choosing a solution for the thread to help others that have similar issues.
Hi Harvey, for some reason I can't seem to find how to mark the solution? Sorry. But it was your apt install suggestion.
The Helpdesk forums contain the ability to mark solutions. Tutorials and Chat and Feedback all do not offer the Solution option as there is no need for it.
Likely, 337harvey forgot that this was in Tutorials.
Which I also do... too often...
I'm curious as to how Firefox is configured. Have you tried uninstalling and reinstalling it? I'm also curious in the amount of RAM you have and the sort of processor you have. Gnome has the ability to handle a big quantity of RAM. It's possible that expanding the swap file size will help, but without understanding more about your system, I couldn't say.
@johnsonwilliam cl20 has posted his specs:
He had an issue with the installed Firefox. After reinstalling it was resolved since his hardware is more than capable of handling it.
I had an issue with the installed Firefox as well...
I installed Firefox from Mozilla and so far haven't had any issues. Just make sure you remove the one currently installed first.
The instructions are on Mozilla's website and very easy to follow, and I used my old profile so I didn't have to reinstall any extensions.