If you’ve recently upgraded to WordPress 2.8 and you’ve noticed that your friendly post editor (WYSIWYG by TinyMCE) no longer appears, you must likely have Google Gears enabled for your site. The Javascript error console includes a line number error and when viewing the script source, unreadable binary characters are present.
To fix, remove your site from the list of sites Google Gears is enabled. To do this from Firefox, click the “Tools” pull down menu and select “Gears Settings”. Click ‘remove’ for the sites listed that are having the problem.
From my research, I’ve discovered that Google Gears Caches files locally without regard to javascript errors, cleared browser cache or taking into account the query strings in the URLs. It may be too complicated for Google Gears to detect javascript errors, but it should detect when the cache has been cleared in a browser in my opinion. More importantly, when the URL changes, e.g. from /wp-includes/js/tinymce/wp-tinymce.php?c=0&ver=3241-1141 to /wp-includes/js/tinymce/wp-tinymce.php?c=0&ver=3241-1141&change=1), Google Gears should treat this new URL link differently, as the query string may tell the server to send back a completely different code.Google Gears Developers: Please treat the URL including the query string as separate files to be cached in Google Gears.
The only way I could see WordPress developers from preventing this from happening in the future is to rename the wp-tinymce.php file for every release. There may be some documentation for Google Gears as well to tell it to upgrade all of the locally cached files.