It's not like that for everybody. If I do this (Firefox running on Ubuntu), my browser switches tabs instead.
For most people the best solution is the US International keyboard layout in its variant without dead keys. The only difference to the normal US layout is that the right Alt key gets the AltGr function. E.g. AltGr+e = é, AltGr+,=ç. (Dead keys means that when you press '`"^~, at first nothing happens. The symbol is combined with the following letter or space, if possible. This is even easier to remember, but most people don't like it when they have to press space to get normal ' and ".)
If you're using Ubuntu (or any other Linux distro), the Compose key is very convenient. You might need to enable it (have a look on Google or dig around in your system settings a bit). Then you can combine any characters that it makes sense to combine - e.g. pressing <compose> then <'> then <e> gives you é, <compose> then </> then <=> gives you ≠, and so on.
basically, oké is the same as ok. the accent means that you make the "e" long as you pronounce it. there is also the "è", as in "blèren". here, you make the e short. shame i can't demonstrate ;) dutch also has the umlaut (kopiëren - to copy), the circumflex (used for french loanwords as gêne - embarrassment), the acute accent (café - cafe) and the grave accent (as in blèren - to yell/cry). hope i haven't forgotten anything ;) the acute accent is also used to place extra emphasis on a word (kom hier, nú - come here, NOW!). bit of a difficult language i'm afraid ;)
Though it doesn't actually have an umlaut, which is a remnant character in German words. Rather, it has a "trema" (diaeresis), which is an indication that a vowel does not form a diphthong with the letter before it.
These two were combined, together with other similar uses, into one glyph, to be able to encode more characters with one-byte characters. Now that larger character sets are possible, people seem to find it difficult to distinguish between them again.