Hi, ya like to confuse things I see.

Is there a reason not using a Great Britain Firefox release ? https://www.mozilla.org/firefox/all/ with a GB Dictionary https://addons.mozilla.org/en-US/firefox/language-tools/ not a language pack unless there is one that will do the characters your looking for and can switch between them.

That would then do away with emulating a mac keyboard.

https://addons.mozilla.org/en-US/firefox/addon/unicode-input/

Just guessing here and looking at other options.

I have set the keyboard in KDE, not in Firefox. Localisation shouldn't affect whether this key is available or not, as em dashes are not unique either to British English or to American English, so I doubt that it would fix this particular issue. The only way to input em dashes other than copying and pasting is to use a keyboard layout that has them; I set the keyboard layout using KDE.

I don't see what you mean by “emulating a mac keyboard”. I can set the keyboard layout in the settings menu of KDE. One of the options produces the same output as a Macintosh international layout. However, it is just as native to KDE as any other layout, e.g., the plain UK layout without internationalisation (I need this to enter diacritics and ligatures), so I don't think that it would affect Firefox.

On Linux you would normally use the compose key to compose the em dashes:

min min min => — (0x2014)
min min period => – (0x2013)

See also:

• https://fsymbols.com/keyboard/linux/compose/
• https://en.wikipedia.org/wiki/Compose_key

I am aware of the compose key, and it works for me, but I was hoping to be able to use the original keyboard layout, since it is faster to type an em dash; this may be the only solution though.