Webmail - I suspect its using an American spell checker.
When I use webmail and compose a message, the spell check picks up "tyre" and "metre" as mis-spelt. Therefore I suspect its using an American spell checker. I compared it using the "Chrome" browser for the same web mail and it accepts these two words as British English. The computer is set up as British English. All my other 5 Linux computers Are OK with the same webmail using Firefox which accept the two words "tyre" and "metre". The problem is on this particular computer setup exactly as the other ones.
SETUP
Linux Mint 18.1 Sarah "Mate"
Firefox 58.0.2 (64-bit)
Private browsing mode (Never remember history)
Languages: "English/United Kingdom [en-gb]" and "English [en]" (Its no different if I remove the "English [en])
Do you have any suggestions as to what's causing the error alert. (red line under the words and right click suggestions)?
Wšykne wótegrona (2)
Hi, make sure you have the 'British English Dictionary (Marco Pinto)' installed - https://addons.mozilla.org/en-US/firefox/language-tools/
Restart Firefox after installing. You should see it in the 3-bar menu > Add-ons > Dictionaries.
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Wót Scribe
The inline spell checker in Firefox is not set to a language as that is due to dictionary in use if any.
https://support.mozilla.org/en-US/kb/how-do-i-use-firefox-spell-checker#w_switching-dictionaries
Wót James