Firefox suddenly displays all pages in completely unreadable font looking like a mix of Asian locales and random symbols, while language/font settings are still correct; internet page display is hence completely broken, restart/reinstall of no help.
As far as I remember I opened a Japanese web page with both EN and JP text in a new tab.
A few mn later, all my (dozens of) tabs suddenly switched to a completely unreadable scramble of symbols, a mix of Japanese and other vaguely Asian characters + apparently random symbols.
I've checked my language/font settings as thoroughly as I could by using a correctly working firefox instance on another computer and navigating through menus in parallel. No visible problem there.
When I print such an unreadable page to a file, it shows correctly in the original language (French or English). When I copy/paste some of the scrambled text, the result is also displayed fine in Latin alphabet.
Restarting firefox doesn't help, with or without saving the tabs.
Todas as respostas (2)
Looks that something is wrong with the font that Firefox uses.
You can try to reset the preferences:
Create a new profile as a test to check if your current profile is causing the problems.
See Basic Troubleshooting: Make a new profile
There may be extensions and plugins installed by default in a new profile, so check that in "Tools > Add-ons > Extensions & Plugins"
If that new profile works then you can transfer some files from the old profile to that new profile (be careful not to copy corrupted files)
See http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox
Thank you very much ;-) In the meantime I just restarted my Ubuntu system and everything works fine again... Very windows-like way of troubleshooting, I fear, but it's worked so far.