Firefox doesn't supports all the codes or this similar bbcode. This may be a bug, are you sure you're using the latest Mozilla client? Try out the beta with better performance or wait for a moderator to solve this problem issue. Thank you for the report. - John.

Mozilla has a Rich Text Editor built into Firefox.
http://www-archive.mozilla.org/editor/midas-spec.html

One simple line of code on the web page enables it.
document.getElementById("edit").contentDocument.designMode="on";

In a rich text editor HTML code (<b>TEXT</b>) should be used and not BBCode [b]TEXT[/b]

Do all visitors that use Firefox 16 have this issue?

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do not click the Reset button on the Safe mode start window or otherwise make changes.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

None of the above helped :( Our forum uses MyCode, a simplified version of HTML. It was working just fine until about a week ago. 3 Other ladies have the same problem. All of us uses FF. When we use another browser like Chrome there is no problem with the formatting tools. If we type the code manually like this "[b]TEXT/b", while using FF it does format the text, but we want to be able to use the formatting tools and not do everything manually. I added a picture of the problem. Maybe it will help to identify the problem.

"Due to a change in Firefox 16.1, when using the editor to insert MyCode you might encounter an issue where the tags are shown as [undefined=undefined]/undefined. This has been fixed in MyBB 1.6.9, but until we release it we have provided a patch for you to apply to your own boards."

http://community.mybb.com/thread-127983-post-926896.html?highlight=Firefox#pid926896

The fix is discussed here - http://community.mybb.com/thread-127322-post-922533.html#pid922533
An administrator of that forum can manually apply that fix, or just wait for the MyBB 1.6.9 update.

Thank you so much. It worked and everything is back to normal.

I didn't have this problem with FF16 but I have a similar problem with 17. I support a web site running DotNetNuke 5.6.3, which includes its own Rich Text Editor. I've been able to edit using the wysiwyg editor for years. Today when I tried to edit a module, I had NO rich text editor although the Rich Text Editor button was checked. All I could see and edit was raw HTML. Suggestions for mybb.com etc. won't help because this site is written in ASP.NET.

I really prefer the FireFox interface but the more often you do things like this, the more time I have to get used to Chrome, which displays the editor just fine.

I have the same problem with a forum which is a Web Wiz originally (though our admins re-coded a lot of things). After updating to Firefox 17, mine and several of our other members' rich text editor stopped working, even though the box was checked in our profiles. It works just fine in Chrome and IE, I checked.

I'm a content admin, not a code admin; does the fix proposed for FF 16 work on this FF 17 problem as well?