Hello,

Try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that turns off some settings and disables most add-ons (extensions and themes).

(If you're using an added theme, switch to the Default theme.)

If Firefox is open, you can restart in Firefox Safe Mode from the Help menu by clicking on the Restart with Add-ons Disabled... menu item:


If Firefox is not running, you can start Firefox in Safe Mode as follows:

• On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.
• On Mac: Hold the option key while starting Firefox.
• On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode
  (you may need to specify the Firefox installation path e.g. /usr/lib/firefox)

Once you get the pop-up, just select "'Start in Safe Mode"

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, and you need to figure out which one. Please follow the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.

To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help others with the same problem.

Thank you.

Thank you, this was a good idea - but unfortunatelly, the situation is the same. I tried several sites with file dialogs (including my own, where I know what happens with it), but in 9 of 10 cases there was considerable lag before the dialog appeared, or after it was confirmed. Sometimes, both. Also, some other laggy behavior didn't dissapear, though I thougt it would. It's actually kind of relieve to see, that my addons are not causing any trouble.

Try to rename (or delete) the mimeTypes.rdf file in the Firefox profile folder to reset all file actions.

• http://kb.mozillazine.org/mimeTypes.rdf
• http://kb.mozillazine.org/File_types_and_download_actions#Resetting_download_actions

You can also check the browser.download prefs on the about:config page.

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) as a test to see if that helps.

Other things that need your attention:

Your System Details List shows multiple Flash plugins.

1. Shockwave Flash 11.9 r900
2. Shockwave Flash 10.0 r45

You can find the installation path of all plugins on the about:plugins page.

You can check the Flash player installation folder for multiple Flash player plugins and remove all (older) version(s) of the plugin (NPSWF32) and (re)install the latest Flash player.

• (32 bit Windows) C:\Windows\System32\Macromed\Flash\
• (64 bit Windows) C:\Windows\SysWOW64\Macromed\Flash\

SOLUTION (your mileage may vary) -- originally posted on a similar post here: https://support.mozilla.org/en-US/questions/991703#answer-618728

I was experiencing precisely the same behavior.

Then, based on a comment by user "mattyjt" over at BleepingComputer (http://www.bleepingcomputer.com/forums/t/505204/file-upload-window-hangs/), I disabled Bluetooth in the Startup tab in Task Manager, then stopped the three Bluetooth services in the Services tab (later, I followed this up with open Services.msc and setting all three to Manual).

That did the trick. Immediately (I didn't even have to reboot), I could use Firefox's file dialog again. Don't know why. But, reasoning out how file dialogs are typically called in programming, and seeing how your issue was resolved by disabling startup items, I began to suspect that it wasn't a Firefox issue, per se, so I began to google around without the word "Firefox", which led me to the BleepingComputer forum linked above. Hope this works for you as it did for me!