I don't think CSS can change a text node (i.e., text between the <title> and </title> tags).

This doesn't work either (attempting to insert text before the existing text):

@namespace url(http://www.w3.org/1999/xhtml);
@-moz-document url("about:home") {
  title::before {
    content: "Hello There -- ";
  }
}

Oh, I see.

I found some CSS code to change text for items on the about: addons page, and so I thought that it might be possible to do something similar for a page title too.

Would it have to be done with javascript? and if so, how?

I'm afraid my javascript skills are as non-existent as my CSS skills.

Thanks.

It's easy to change the document title with JavaScript:

document.title="Hello Friend";

However, Greasemonkey might not run on about:home. https://wiki.greasespot.net/Include_and_exclude_rules#Greaseable_schemes

Maybe there is a different add-on to modify the title?

You might try this forum, as their CSS hacking skills are more advanced than mine: https://forum.userstyles.org/discussions

Thanks for the clarification and link.

I was hoping that it would be simple to achieve with GreaseMonkey, but apparently not (due to 'about' pages being excluded).

I will try the userstyles forum as you suggest. I have had very helpful replies there in the past.

Quisquose said

I will try the userstyles forum as you suggest. I have had very helpful replies there in the past.

I spoke too soon!