I also have this problem. It just started today out of the blue. Whenever I hit "attach file" in gmail, I never get a "file explorer" popup. Simply nothing happens.

• I'm running 31.0 on Mac 10.8.5.
• I have tried resetting firefox several times. I've tried restarting in safe mode multiple times. Nothing will allow the window to appear.
• I've tried various (old) fixes I found through searching (mostly involving about:config settings) but none worked.
• Drag and dropping files onto a note DOES work (but this is no solution!).
• I have cleared the cache several times but to no avail
• I don't have the stomach (or time) now to completely uninstall and re-install. Not yet anyway.
• This function works fine in Chrome and Safari

I finally went and UNCHECKED popup blocking. Now I get the file popup immediately! So it would seem that somehow Firefox is blocking the file "finder" interface as a popup. What gives?

Google is very innovative with their scripting and they seem to have tripped something unexpected in Firefox because normally you get an info bar above the page when pop-up blocking is an issue.

Anyway, you can keep the pop-up blocker enabled generally and make an exception just for Google. Here's how:

While you have the compose window on the screen, click the padlock in the address bar.

• If the pop-up permission is listed there as Block, try changing it to Allow.

• If the pop-up permission is not listed there, click More Information to launch the Page Info dialog, then click Permissions in the top bar. Scroll down to "Open pop-up windows", uncheck the box for "Set default" then click Allow and close the dialog.

Then try the paper clip again. Success?

Unfortunately, that is "Google-wide" and not limited to mail, so... other pop-ups are possible that you've never noticed before.

Google indicates on their forums that they're working on fixing this, so you might check in a couple days whether you can block pop-ups on Google again.

I stumbled across a similar solution I believe by adding mail.google.com to the popup "exceptions" list. It worked to enable the popup from compose though I don't know whether there would have been a side effect elsewhere. I've since removed the exception and configured it as you describe above. Thanks!

That was a good attempt, but the shot went wide of the net. The check mark for the default on open pop-up windows was checked, and the grayed-out radio buttons for that item indicated block.

So how is the shot wide? The paper clip returned to normal function today. No idea why.

Good info you provided, it will help others, and maybe me later. You are the one, thank you!

Screen shows the permissions set to block but the paper clip is working.

I added gmail to the pop up block exceptions, but when I did that it did not fix the problem.

Overnight, it fixed itself. Go figure.

In my case, the solution was to let it fix itself while I slept, similar to the manner in which the problem was created. I do not recommend this as a solution, but I can say this is how my problem was fixed.

Prior to sleeping, I agonized the whole day, trying every suggestion I could find, but all to no avail. I cannot say that had an impact on the solution or not, but I am thinking agony might be required before this will fix itself. Hard to say, I don't remember doing anything to cause the problem.

Good luck and may the wind blow at your back.