Hi,

The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. Note: This will cause you to lose any Extensions, Open websites, and some Preferences.

To Reset Firefox do the following:

1. Go to Firefox > Help > Troubleshooting Information.
2. Click the "Reset Firefox" button.
3. Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
4. Firefox will open with all factory defaults applied.

Further information can be found in the Refresh Firefox - reset add-ons and settings article.

If the problem persists, you can also try to Disable all the plugins except Flash and Java to check.

Did this fix your problems? Please report back to us!

Thank you for the response.

I probably should have mentioned: this problem occurs on multiple computers (my home computer and two different work computer), which led me to believe it was an issue with Firefox generally rather than with my individual machine.

dumdidadida's suggestion didn't exactly solve my problem, but allowed me to isolate the reason it is happening.

After I reset Firefox, I immediately visited Facebook and everything worked properly (drop-down menus, messages, etc.). I thought, "Great, problem solved!" and then went into Tools > Options to set up Firefox with my usual settings. After doing this, I went back to Facebook and it no longer worked properly.

Long story short, I went through all of my settings carefully and discovered the one setting that makes the difference in how Facebook works. Under Tools > Options > Privacy, you can choose how your browser accepts cookies or not. If you choose to accept cookies, you can also choose how long your browser stores them, using the "Keep until" drop-down menu. I discovered that if I choose "Keep until: they expire," Facebook works properly, but if I choose "Keep until: ask me every time," Facebook does not work properly-- even if, when prompted, I choose to allow cookies from www.facebook.com.

Now that I've identified this cookie setting as causing the Facebook issue, I'm assuming there isn't an easy fix-- I can either choose "Keep until: they expire" or I can just choose to use Chrome when I want to use Facebook.

A question for someone who knows more about computers than I do: is this a problem that could be solved by Facebook making changes to their website, or is this a problem that could be solved on Firefox's end?

I noticed the exact same issue. For security reasons, I do not want to allow cookies to be installed automatically, which is why I choose to use the "ask me every time" option. However, with FF16 (and some versions of FF15) breaking FB compatibility (at least from my perspective), it will force me to use IETab, IE, or Chrome. Any of these three options is an inconvenience for me, as FF is my preferred browser.

Hopefully Mozilla will fix this incompatibility soon.

You need to go to Privacy Show cookies, then search for Facebook.

Shift-select all Facebook cookies and click Remove Cookies, Not Remove ALL.

Then click on exceptions, type in facebook.com and set to allow

Thanks! I just did this, and now Facebook messaging and the drop-down menu both work.

To be honest, I'm not sure why this fixed the problem-- I had already gone into my list of exceptions and set www.facebook.com to "Allow," but for some reason adding facebook.com and setting it to "Allow" solved the problem.