I am not able to add Firefox add-on
When I click on extension there is no option to go on find more add one
And even when it comes sometimes (rarely) then website don't open it keeps reloading
Please check with Mozilla Support and see if you can troubleshoot;
https://support.mozilla.org/en-US/kb/unable-install-add-ons-extensions-or-themes
Firefox is compatible with almost every Operating System (Android, Windows, Mac, Linux) and distro and is installed on most of them. It is an independent project and while some distros may include it, they do not have control over it.
It is perfectly reasonable to ask on here, in case anyone else using Zorin or is a member of this board has experience with that issue and has resolved it. But your best bet for help will be Mozilla Support.
How did you install Firefox. Was it part of your original Zorin package or did you install it from Software Store?
If the latter, was it the Snap version you installed?
It was A part of zorin Package but now that problem is solved by now I am not able to play video on YouTube?
Your referencing is tantamount to cross-posting. Please don’t do that - it violates forum rules: FAQ - Zorin Forum
Zorin comes pre-installed with Firefox and Addons have no problem with the packaged version. The pre-installed version is already present in the taskbar right next to the Zorin “Z” start menu in the bottom left corner. There is no need to install it from any other source. You have either installed a snap version (as Zab noted) or a Windows version (using Windows App Support). If you continue to use the non-pre-installed version, please check on the Mozilla support forum, as recommended by Aravisian.