The new "menu in the upper left" seems to be rather badly designed. It's missing the "View" menu entirely, which makes it impossible for me to view non-ASCII/Unicode websites. It took me about 5 minutes of searching and frantically right-clicking to re-enable the old menu, which of course still had the View menu.
On a positive note, 4 is so much faster than 3.6 it isn't even funny. It's like going from a 286 running off of an 8-inch floppy to a Core 2 on an SSD.
Character encoding options are now in the "Web Developer" sub-menu of the Firefox menu. (Weird, I know.)
UPDATE: This is different in localized builds - Japanese builds of Firefox should provide easier access to the encoding menu. In other locales, you can go to about:config and toggle "browser.menu.showCharacterEncoding" to see this.
You can also press Alt+V to quickly open the old View menu.
I'm a user of such a language (Arabic) and by now all websites I care about use utf8, so the character encoding is a problem from the past as far as I'm concerned.
I'd be really surprised if there are still sites that don't use utf8.
I visit some Japanese websites from time to time (not that I can read or anything .. just clicking on links) and don't remember having many problems with weird characters.
On a positive note, 4 is so much faster than 3.6 it isn't even funny. It's like going from a 286 running off of an 8-inch floppy to a Core 2 on an SSD.