XMLHttpRequest to Opera Link (link.api.opera.com) gives Bad Request in Firefox

Hello!
I am writing an extension to synchronize bookmarks with Chrome, Firefox and Opera. I currently use Google Bookmarks and Opera Link. Opera Link works in Chrome, but not in Firefox (Firefox gives a 400 Bad Request). The code is the same, so that shouldn't be the problem. I think the problem lies with the difference in headers:

Firefox:
POST /rest/bookmark/ HTTP/1.1
Host: localhost:8123
User-Agent: Mozilla/5.0 (Ubuntu; X11; Linux x86_64; rv:8.0) Gecko/20100101 Firefox/8.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip, deflate
Connection: keep-alive
Authorization: OAuth realm="",oauth_consumer_key="immqSD074yPY83JWSKAzmjUUpOcC7u40",oauth_token="AT3dpXXXXX",oauth_version="1.0",oauth_timestamp="1318679723",oauth_nonce="A4XXXXX",oauth_signature_method="HMAC-SHA1",oauth_signature="F8IItHXXXXXXXXXXXXXXXX"
Content-Type: application/json; charset=UTF-8
Content-Length: 96
Pragma: no-cache
Cache-Control: no-cache

Chrome (Chromium) (I know it doesn't have the POST header):
Accept:*/*
Accept-Charset:ISO-8859-1,utf-8;q=0.7,*;q=0.3
Accept-Encoding:gzip,deflate,sdch
Accept-Language:nl-NL,nl;q=0.8,en-US;q=0.6,en;q=0.4,eo;q=0.2
Authorization:OAuth realm="",oauth_consumer_key="immqSD074yPY83JWSKAzmjUUpOcC7u40",oauth_token="ATI5XXXXXXXXXXXXXXXXXX",oauth_version="1.0",oauth_timestamp="1318679566",oauth_nonce="IcJXXXX",oauth_signature_method="HMAC-SHA1",oauth_signature="cNYXXXXXXXXXXXXXXXXXX"
Connection:keep-alive
Content-Length:90
Content-Type:application/json
Cookie:__kti=1304508457014,http%3A%2F%2Fwww.opera.com%2Fdocs%2Fapis%2Flinkrest%2F,; __ktv=9eb6-27f0-58c0-4d112fbac36039; language=en; __utma=122269525.1612809356.1304508454.1309807876.1318593402.12; __utmz=122269525.1318593402.12.5.utmcsr=google|utmccn=(organic)|utmcmd=organic|utmctr=opera%20link%20bad%20request
Host:link.api.opera.com
Origin:chrome-extension://dbbmibbibfblebmomaphijkkpbhfoemj
User-Agent:Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/535.1 (KHTML, like Gecko) Ubuntu/11.10 Chromium/14.0.835.202 Chrome/14.0.835.202 Safari/535.1

I think that the problem is that Chrome just uses the Content-Type:application/json header, and that firefox appends '; charset=UTF-8' at the end of the Content-Type (which Opera Link should understand, according to http://forums.mozillazine.org/viewtopic.php?p=6318215#p6318215). So, am I right and handles the Opera Link server the Content-Type header in a wrong way, or is there another problem?

I use a test account (it's much easier to just test a few bookmarks and not the whole list in my real account, and I don't want to mess up my bookmarks): test-vantester.

Another note: authorizing and getting bookmarks works just fine. Only POST requests don't work.

EDIT: it's indeed the appended charset that gives the error. I tested it in Chrome. When I appended '; charset=UTF-8' the server gives a Bad Request (which it shouldn't).

*bump*

If my question wasn't clear: can this be fixed in Opera Link or is there a workaround?

Well, I found a solution for this. When using xhr.sendAsBinary, Firefox doesn't send the charset option. But it only accepts Ascii data, other data will be escaped. So I also have to escape the data. See https://github.com/aykevl93/Sync2all/blob/master/chrome/content/operalink.js#L288
The main page of the extension is here: https://github.com/aykevl93/Sync2all
It works best on Chrome and also mostly on Firefox.