Working on a Mac using Safari and Firefox, I recently had exactly the same problem after moving a website from developing server to live server (from another provider). After that I could only upload images with a file size of max. 200 KB, while max upload file size set by the provider was 16 MB.
In Internet Explorer 8 I had no problems uploading larger files. In that browser the AJAX-uploader (with drag-and-drop functionality) isn't supported, instead the 'classic' uploader is used. So I thought the AJAX-uploader should be the problem. I solved the problem after editing line 296 of InputfieldFIle.js (wire/modules/Inputfield/InputfieldFile/) from:
InitHTML5();
into:
InitOldSchool();
Strange thing is that this problem only shows up at some providers...
Didjee's post in image upload gettings stuck on 100% was marked as the answer