Show us the issue. Also, provide steps to replicate if possible and hide any personal info.

Please explain the problem in detail. What happens? What is/are the exact error message(s) ?

Make sure you are not blocking content.

https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop also see https://blog.mozilla.org/security/2021/03/23/introducing-smartblock/

https://support.mozilla.org/en-US/kb/smartblock-enhanced-tracking-protection

Diagnose Firefox issues using Troubleshoot(Safe) Mode {web link}

A small dialog should appear. Click Start In Troubleshoot(Safe) Mode (not Refresh). Is the problem still there?

Many site issues can be caused by corrupt cookies or cache.

Warning ! ! This will log you out of sites you're logged in to. You may also lose any settings for that website.

• Delete cookies to remove the information websites have stored on your computer {web link}

• How to clear the Firefox cache {web link}

When I sign in to QBO and each time I press any link, such as a client from list or any items on menus with in QBO I get an error message: This page is slowing down Firefox. To speed up your browser, stop this page

Obviously this isn't workable, my only option is to then use another browser which I have been doing but prefer to stay in Firefox. Any advice would be wonderful!

Actually refreshing Firefox from the Troubleshoot option solved the problem, Thanks!

That was very good work. Well Done. Please flag your last post as Solved Problem as this can help others with similar problems. Go to that post and click the 'Solved' button to its right.

Cool. Mark your comment as resolved and get back to the books.  ;-))