You did not list what you already tried, so . . . . Make sure you are not blocking content.

Start Firefox in Safe Mode {web link}

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

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

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}acking-protection-firefox-desktop

What content is blocked ?

You can check the Web Console (Tools -> Web Developer) for messages about blocked content and about the presence of mixed or unsafe content.

• https://developer.mozilla.org/en-US/Tools/Web_Console

You can check the Network Monitor to see if content is blocked or otherwise fails to load.

• https://developer.mozilla.org/en-US/Tools/Network_Monitor

If necessary use "Ctrl+F5" or "Ctrl+Shift+R" (Mac: Command+Shift+R) to reload the page and bypass the cache to generate a fresh log.

I am having various problems. For instance, Captcha doesn't work, some websites don't work properly or don't open a window.

I have tried starting up in safe mode and that appeared to solve the problems. I then did a Refresh and restarted Firefox, but the problems were still there.

I've looked at web console, but that far too advanced for me. I tried looking at the network monitor while I clicked on a web page that doesn't work, but it only produced one line that doesn't seem to show any errors.

I've deleted cookies, cleared the cache, but just don't seem to be getting anywhere. Is it possible to regress to an earlier version of Firefox. It used to work fine and is my preferred browser, but it's no use to me as it is.

It could be the work of one of your add-ons, or it could be Hardware Acceleration. How to disable Hardware Acceleration {web link}

Type about:addons<enter> in the address bar to open your Add-ons Manager. Hot key; <Control> (Mac=<Command>) <Shift> A)

In the Add-ons Manager, on the left, select Extensions. Disable a few add-ons, then Restart Firefox.

Some added toolbar and anti-virus add-ons are known to cause Firefox issues. Disable All Of them.

If the problem continues, disable some more (restarting FF). Continue until the problem is gone. After, you know what group is causing the issue. Re-enable the last group ONE AT A TIME (restarting FF) until the problem returns.

Once you think you found the problem, disable that and re-enable all the others, then restart again. Let us know who the suspect is, detective.

Thank you Fred, that seems to have fixed the problem with at least one of the websites that stopped working correctly. It was caused by the Extension DuckDuckGo Privacy. I'm now waiting to see if any problems keep cropping up (especially the Captcha one) before marking it as Solved.

Regards, Edward

Glad to help. Safe Surfing.