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Can't open Firefox after update.

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I've asked similar question before: https://support.mozilla.org/en-US/questions/1281058

Unfortunately it didn't get any replies. I hope this one get replies because this time I really can't seem to fix it.

I can't open Firefox after it's automatically updated to 74.0. I tried to reinstalling like I did before when 73.0 problem happened, but it's not working at all.

I get two kind of messages when I tried to reinstall. See attached images.

Please help because I'm seriously frustrated, encountering this problem over and over.

Attached screenshots

Modified by evithewriter

All Replies (5)

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Try a Clean Reinstall:

To do a clean reinstall of Firefox, please follow these steps. Note: You might want to print these steps or view them in another browser.

Download the latest Desktop version of Firefox from mozilla.org (or choose the download for your operating system and language from this page) and save the setup file to your computer. After the download finishes, close all Firefox windows. Delete the Firefox installation folder, which is located in one of these locations, by default: Windows: (Note: Check both folders.) C:\Program Files\Mozilla Firefox C:\Program Files (x86)\Mozilla Firefox Mac: Delete Firefox from the Applications folder. Linux: If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it - see Install Firefox on Linux. If you downloaded and installed the binary package from the Firefox download page, simply remove the folder firefox in your home directory. Now, go ahead and reinstall Firefox: Double-click the downloaded installation file and go through the steps of the installation wizard. Once the wizard is finished, choose to directly open Firefox after clicking the Finish button.

More information about reinstalling Firefox can be found here.

WARNING: Do not use a third party uninstaller as part of this process. Doing so could permanently delete your Firefox profile data, including but not limited to, extensions, cache, cookies, bookmarks, personal settings and saved passwords. These cannot be easily recovered unless they have been backed up to an external device! See Back up and restore information in Firefox profiles.

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Hello RobertJ,

I've followed your instruction, but after clicking the Finish button, Firefox still won't launch, my cursor keeps blinking, and even if I want to end the process through the Task Manager, it won't let me because the process disappear and reappear too fast for me to click at it.

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Try this: Shut your computer down and wait a few minutes, then,

Start your computer in Safe Mode -

How to Start Windows 7 in Safe Mode https://www.lifewire.com/how-to-start-windows-7-in-safe-mode-2624540

While in Safe Mode, Delete the Firefox installation folder: Windows: (Note: Check both folders.) C:\Program Files\Mozilla Firefox C:\Program Files (x86)\Mozilla Firefox

Restart your computer in normal mode and install Firefox.


If you continue to have issues, you probably have Registry problems in Windows 7.

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I've tried it and it's not working.

By Registry problem, could it be you're talking about the one in the attached picture?

Can you please tell me how to resolve it?

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Hi, so I decided to tackle the Registry problem by following the instructions here: https://answers.microsoft.com/en-us/windows/forum/all/microsoftc-register-server-has-stopped-working/37dc4ffe-4b5e-4a8a-b050-0d00e640bb77

Then afterwards I tried installing ver 75.0 but it's the "Microsoft(C) Register Server has stopped working" thing still appears.

Can anyone please suggest another solution to this?

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