remoulder wrote:The language settings for firefox are independent of the system settings, you need to install the relevant language add-on in FF.
OK, I find . . . nothing . . . in Preferences about setting the language independently of the system settings.
Where would I find that information?
Update: 12:44 MDT
I also checked in the synaptic package manager and found the I DO have the English language package for Firefox installed.
I'm still looking for why it changes from US English to UK English (BIG differences in spelling for the spell checker) at seemingly random intervals.
Edit 7/3/12: 04:12 MDT
Tried using Libre Office Write and it also had the US English changed to UK English.
Most US people do not really like the Euro spelling, in US documents.
I am also on M13/MATE. It bothered me so much as I am a Biblical studies student and so have Greek and Hebrew installed... so it used the Greek spell checker, weird, huh? and so everything was red-squiggled. In Firefox's Edit-->Pref-->Content-->[Language] Choose, I had English installed as Default language. But it still didn't remember the language. So what I ended up doing was disabling all the language dictionaries in Tools-->Add-On-->Languages. STILL HAD GREEK AS SPELLCHECKER!! GRRR...
Then, I went to MintMenu-->Language Support and, I moved my Greek language, to the end (and it may be in faded gray font, but I moved it nonetheless), even though English-US was on top. I then "refreshed" by clicking on Apply System-Wide (though I did that before), and now, somehow my Firefox is finally working well using English-US. I.e. theatre is red-squiggly-marked, so I know that it's not British English or something.
So basically, this worked for me:
Check Firefox Default Language (under Edit-->Preferences-->Content-->Choose).
THEN go to Add-ons and disable any and all non-English US (or whatever dictionary) and restart [and, if after all this your language checker still doesn't work, then possibly make sure it was English (make sure you have an English-US dictionary installed via Firefox Add-Ons]
THEN go to MintMenu-->Language Support, and make sure English-US is on top of the list and then hit Apply System-Wide.
Hopefully that should do the trick. It did for me. Finally, not seeing red-squiggles under every word, because it's not GREEK! (because I'm typing in English!!!)