macOS 10.13.6 (High Sierra) on a MacBook Pro is quite an older operating system.

You may want to use the Firefox ESR version.

You can also try this: 1. Type about:config in Firefox's address bar and press Enter 2. Click through the warning prompt 3. In the search bar on that page, type: dom.event.clipboardevents.enabled 4. If this value shows as "false", click the toggle button to change it to "true"

Good luck.

I now find it's possible to copy and past one line at a time, and sometimes a few lines at a time! How crazy is that?

Thank you Wxie. Sorry, before seeing your comments I posted again: "I now find it's possible to copy and past one line at a time, and sometimes a few lines at a time! How crazy is that?" Does this sound like something your advice would fix? I'm obviously hesitant to get involved in things I know nothing about like coding and Terminal etc.

Or you can start trouble shooting mode and try it. You can always change it back to it original value.

https://support.mozilla.org/en-US/kb/reset-preferences-fix-problems

Thanks again Wxie! I'm now realising the problem is limited to the AI-generated text in Google. You ask a question and Google's AI offers an answer; copying that text is painstakingly difficult (as described). However, I've now discovered if I copy and paste the WHOLE PAGE it will include the AI-generated text at the top! So it seems the issue might not be in my laptop but in the way the AI text is formatted? Any thoughts?

I am not sure what's the problem. Google docs sometimes cause problem in Firefox for copy/paste. The solution was provided above.

What AI do you use? I think the UI should have an icon for copying all the AI answers so that you do not need manual copy.

Hi wxie, Your support is much appreciated! I'm grateful for the steps you've advised me to take, which I'll follow up on. I'm sorry you didn't understand my last comment. You asked 'What AI do you use?' I'm not using any AI app. I go to the standard google (search engine) page online and ask a question. The answer (generated by AI?) is given at the top of the page. I posted that it's difficult to copy and paste the text of the answer. However I now find that if I copy and paste the WHOLE PAGE it will include the AI-generated text at the top of the page! So it seems the issue might not be in my laptop but in the way the AI text is formatted? Any thoughts? Hope my comment is clear now?

Most of the AI interfaces either respond iteratively over time, or with controls to refine the interactions that end up interfering with the actual pointer if you try to select and copy the responses.

A lot of them acknowledge the problem by providing a dedicated "Copy" button, like here in Google's AI instance:

Thank you for your helpful comment and attachment jbr. Unfortunately a dedicated "Copy" button doesn't seem to be provided on the standard online google (search engine) page. As you say, selecting and copying google responses can be problematic. However, as I've posted, if the whole page is selected and copied it will include all the response text! Is there a plausible explanation for this behaviour?

A lot of interactive elements, like this auto-expanding text content, are controlled by the site, and might prioritize mouse events for opening/closing, unhiding and collapsing the sections — which then makes it extremely hard to select text for copying and sharing.

As you noticed, the best workaround is usually just to select more of the content, even outside of the stubborn element, and the summary will be included without having to wrestle the actual panel that gets in the way.