Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

Same problem in Safe mode.

Separate Security Issue: Update your Flash Player Note: Windows users should download the ActiveX for Internet Explorer. and the plugin for Plugin-based browsers (like Firefox).

Note: Windows 8 and Windows 10 have built-in flash players and Adobe will cause a conflict. Install the plugin only. Not the ActiveX.

Flash Player Version: 25.0.0.171

https://get.adobe.com/flashplayer/ Direct link scans current system and browser Note: Other software is offered in the download. <Windows Only>

https://get.adobe.com/flashplayer/otherversions/ Step 1: Select Operating System Step 2: Select A Version (Firefox, Win IE . . . .) Note: Other software is offered in the download. <Windows Only> +++++++++++++++++++ See if there are updates for your graphics drivers https://support.mozilla.org/en-US/kb/upgrade-graphics-drivers-use-hardware-acceleration

What you describe sounds like the computer's CPU is being overworked. Normally, Firefox does not freeze like this. "Transferring data from" should not be a problem, even if the transfer is having an issue.

Please provide public (no password) link(s) that we can check out. No Personal Information Please !

Start your Computer in safe mode. Then start Firefox. Try Safe websites. Is the problem still there?

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode Starting Any Computer In Safe Mode; Free Online Encyclopedia

Same problem in IE and using a different Internet connection. I'll try using a different computer.

FredMcD said

Start your Computer in safe mode. Then start Firefox.

When Firefox is in the connecting state then this might run on the main thread and this can cause Firefox to be unresponsive. Once the connection has been established (waiting and transfer messages) then Firefox should be responsive again.

Does this happen in the tab where Firefox is busy or are you using the mouse in another tab? Are you clicking in the user interface (toolbar area) or on the web page (browsing) area?

Just had Firefox crash (after working OK for a while) while "Transferring data from connect.facebook.net". Clicking repeatedly on scroll bar brought up "Not Responding" in program title bar and whited-over the page display, but further clicks did nothing. Had to close Firefox using Task Manager, which showed it was using 25% of CPU time. I re-opened Firefox without resetting the WiFi connection and now it's working fine (while I'm typing this). Since I got the "not responding" system message, the problem must be in Firefox.

The problem is caused by a slow Internet connection that has spells of non-responding. However, it is a programming error in Firefox to ignore user clicks and commands while transferring data or waiting for a connection. It is also an error to omit a time-out on any Internet transaction. The time-out should be part of the protocol, so EVERY transmission has a time limit. May I also point out that Firefox, like many programs, is so slow to start that it needs a splash screen just to show that it is opening.

Isn't it ridiculous that we have gigahertz processors, gigabytes of RAM, and have to put up with slow and unresponsive programs that would never have been tolerated in the Windows 98 days? Not to mention webpages that are so bloated and use so much offsite referencing that they are considerably slower (and flakier) than dial-up. You may remember that Firefox was originally a smaller and faster version of the Mozilla browser. We now need a smaller, faster, stripped-down version of Firefox.

Firefox got lost again, and had to be closed in Task Manager. How can a program be distributed world-wide that will not even close at the user's command? Apparently the pop-up "update available" screwed up the Java Script program the webpage was running. When I finally got Firefox off the screen and restarted it, it tried to restore the webpage it crashed on. Of course it started not responding. So if Firefox crashes, it will automatically go to the bad script page next time you open it. Pointy-headed programming.

Close Firefox. Wait about 20 seconds for Firefox to finish closing. Right-click on the Firefox icon and select Open New Window.

Sometimes this works. If it opens, close it by Menu > File > Exit. This will flush out that web page from the Session Store.

Let’s do a full clean re-install; Download Firefox For All languages And Systems {web link}

Save the file. Then Close Firefox.

Using your file browser, open the Programs Folder on your computer.

Windows: C:\Program Files C:\Program Files (x86)

Mac: Open the "Applications" folder. https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac

Linux: Check your user manual. If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it. See Install Firefox on Linux; https://support.mozilla.org/en-US/kb/install-firefox-linux

If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory. http://www.mozilla.org/firefox#desktop ++++++++++++++++++++++++++++ Do Not remove the profiles folder.

Look for, and rename any Mozilla or Firefox program folders by adding .old to them. Do not rename the Mozilla Thunderbird folder if there is one.

After rebooting the computer, run a registry scanner if you have one. Then run the installer. If all goes well, remove the OLD folders when you are done. +++++++++++++++++++++++++++ If there is a problem, start your Computer in safe mode and try again.

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode This shows how to Start all Computers in Safe Mode; Free Online Encyclopedia

I did uninstall, download, and install Firefox again. Same result. Also same result on a different, brand-new computer. The pages that crash are realtor.com and zillow.com.

https://support.mozilla.org/kb/Clear+Recent+History#w_how-do-i-remove-a-single-website-from-my-history

Remove History For One Site

Open the History Manager <Control><Shift> H. In the search bar, enter the name of the site. Right-click on one of the listings and select Forget About This Site. This should remove all information, including any passwords / settings.

Removed history as directed. Opened realtor.com, typed in address, hit Search. Page came up for that address, hung on "waiting for", spinner in tab header "Connecting" stopped. Firefox ceased responding. "Not responding" in program header, Windows dialog box came up after several clicks, closed program. Another dialog box saying "Plugin container has stopped working", closed program. So apparently the Plugin Container can't handle clicks while a data transfer is hanging.

https://support.mozilla.org/en-US/kb/troubleshoot-issues-with-plugins-fix-problems

https://support.mozilla.org/en-US/kb/warning-unresponsive-plugin

The only plugin I have activated is a codec. There is no video content on the webpage that crashed. Shockwave is Ask to Activate and I never get that prompt. So why is the Plugin Container even running, much less crashing? May I also point out that I get the same problem (Firefox becoming non-responsive when a data transfer hangs) on a different computer using the same WiFi connection.

about:crashes has no info on these crashes. Apparently a forced close from Task Manager doesn't count as a crash, nor does being closed from the Windows box "Firefox is not responding". Another programming error. Is there a Page Transitions parameter I can set to 1) prevent any of a page from displaying while its data transfers are incomplete and 2) set a timeout on loading the page?

I called for more help.