Bookmark the following if you want to switch the textareas in a page to a right-to-left direction. This helps when writing Arabic.

أضف الرابط الى علامات الوب فى متصفحك. سوف يقلب الكتابة من اليمين الى اليسار فى أماكن تحرير النصوص. مفيد عند أضافة نعليقات بالعربي.

Update: Now it toggles between the direction of the textarea and uses the DOM to do it, instead of inserting it in the CSS. This also means that it now works on IE too. It switches all the textareas in a page. The bookmarklet produces a harmless JS error in your JS console that is not a big deal. If you can improve on it please do.

Click on it to test it. Or click ALT+R
أهلا يا دنيا!

Doesn't work with complicated Javascript textareas like Gmail.