Hi, please run this https://www.malwarebytes.com/mac/ and download Firefox from here : https://www.mozilla.org/firefox/all/ I am taking that the latest version you mention is 59.0.2 Please let us know if this solved your issue or if need further assistance.

This did not help either. Same result as earlier.

Does the icon show up in the computer's taskbar?

Some problems occur when your Internet security program was set to trust the previous version of Firefox, but no longer recognizes your updated version as trusted. Now how to fix the problem: To allow Firefox to connect to the Internet again;

• Make sure your Internet security software is up-to-date (i.e. you are running the latest version).
• Remove Firefox from your program's list of trusted or recognized programs. For detailed instructions, see

Configure firewalls so that Firefox can access the Internet. {web link}

This didn't help. When clicking the firefox icon, it will not appear on the task bar (if it's not pinned there already). Only reaction is that it will appear in the Task Manager processes list. It seems that there is no issue with the firewall.

This issue started suddenly in December, when I had a laptop with Win7... I thought it would dissappear when changing to Win10 (and new laptop), but situation is the same. I'm using a company laptop, but many of my colleagues have Firefox without any problems. I have tried to install the latest verion also at home connected to my home network, but result is the same.

Start your Computer in safe mode with network support. 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

Unfortunately I'm not able to start in safe mode as this is corporate laptop and it is asking the Bitlocker key when trying to enter to safe mode.

This starts to be quite tricky... I can't understand how firefox can be seen in the processes list when the application itself is not starting at all. And why not any error messages etc.? I've been discussing with my colleagues and one has had the same issue, but in some stage it has disappeared and now he has the latest version up and running. Unfortunately he has no idea what he did to fix that issue.

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 ++++++++++++++++++++++++++++ Look for, and remove any Mozilla or Firefox program folders. Do not remove the Mozilla Thunderbird folder if there is one.

Do Not remove any profile folders.

After rebooting the computer, run a registry scanner if you have one. Then run the installer. +++++++++++++++++++++++++++ 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

No changes...

Use these links to create a new profile. Use this new profile as is. Is the problem still there?

http://kb.mozillazine.org/Profile_folder_-_Firefox#Navigating_to_the_profile_folder

https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible

https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Type about:profiles<enter> in the address bar.

Not able to run Firefox, so it is not starting in profile manager mode either. Tried also create a new profile manually but without success