Here is the fix to overcome the Facebook zoom problem in the iPad. It involves running a JavaScript on the Facebook page to alter their setting. You will need to load this JavaScript into a bookmark then run it any time you reach a page where you want to zoom. Please note that this must be rerun every time you refresh or visit a new page on Facebook.
1) create a bookmark of any random page and name it something like "Facebook Zoom". The name isn't important.
2) once you have the bookmark, go to your bookmarks and choose "Edit" then select then new bookmark you created.
3) erase all the text from the address field that appears right below the bookmark name in the editor.
4) copy the following text exactly as it is, then paste it into the Address field.
javascript:var meta;if (document.getElementsByTagName) {meta = document.getElementsByTagName('meta')[0];if (meta) {meta.name = 'viewport';meta.content = 'device-width, initial-scale=1, maximum-scale=10.0, minimum-scale=1, user-scalable=1';}}
5) press the Bookmarks button at the top of the editor to return to the bookmarks list.
6) press the "Done" button.
7) the next time you need to zoom a Facebook page, go to your bookmarks and click your new link. You will not see a visible change in the page, but you will now be able to zoom.