Proposed rewrite:
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Why can't I use JavaScript, Flash, or certain videos on LiveJournal?
You cannot use scripting languages (such as JavaScript) or embed objects (such as Flash or most videos) on LiveJournal. Because this code could pose a security risk to other users, they are stripped from your custom styles, overrides, entries, comments, and user bio before they are sent to a web browser.
* Scripting Languages: Scripting languages can be used to retrieve other users' browser cookies, which can compromise the account security for any user who views the page. Developers have investigated alternate ways of allowing these languages, but haven't found a way to allow "safe" scripts while blocking those that create security risks.
* Embedding Tags: LiveJournal prohibits use of several HTML tags: <iframe>, <embed>, <object>, and some attributes of the <div> tag. Due to these restrictions, it is not possible to embed music, most videos, or other active content such as Flash objects into journal entries. LiveJournal does allow the posting of video content from YouTube and Photobucket. If you would like to post entries with music or video files from another source, you will need to upload the files to another site and provide a text link to them.
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Alternately, use the following:
* Embedding Tags: LiveJournal prohibits use of several HTML tags: <iframe>, <embed>, <object>, and some attributes of the <div> tag. Due to these restrictions, it is not possible to embed music, most videos, or other active content such as Flash objects into journal entries. LiveJournal does allow the posting of video content from YouTube and Photobucket as described here. If you would like to post entries with music or video files from another source, you will need to upload the files to another site and provide a text link to them.