Note: this post was accidentally marked as a duplicate.

Pkshadow said

Continue this here please https://support.mozilla.org/en-US/questions/1212998

The OP in the above mentioned thread is 'ronde79' - different
question .....

Hi there,

Apologies for marking this question as a duplicate, I will try to answer you question in the meantime.

To correct the issue, I would do a clean reinstall. You may also want to remove the old profile if that was infected with the virus.

Certain Firefox problems can be solved by performing a Clean reinstall. This means you remove your Firefox program files and then reinstall Firefox. This process does not remove your Firefox profile data (such as bookmarks and passwords), since that information is stored in a different location.

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.

1. 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.
2. After the download finishes, close all Firefox windows (or open the Firefox menu and click the close button ).
3. Delete the Firefox installation folder, which is located in one of these locations, by default:
   • Windows:
     • 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.
4. Now, go ahead and reinstall Firefox:
   1. Double-click the downloaded installation file and go through the steps of the installation wizard.
   2. 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.

Please report back to say if this helped you!

Thank you.

sbillups said

For the past 3-4 months, every time I download and install Firefox on any of my Macs my virus software detects a Trojan Flashback Virus!?! When I remove the virus, Firefox will no longer open. I first noticed it when I downloaded the 59.0 beta! The most recent version with that installs a virus on my system is 59.0.2. Can you please help?

Where are you downloading Firefox for Mac from as is it www.mozilla.org/firefox/all/ ?

You have to be careful with third-party download sites as a while ago the MacUpdates site was affected by a hack of sorts in which some listed apps had their downloads changed to a modified version. For a brief time the site had the Firefox 58.0.2 download changed to a version that had been modified with a crypto minor tool built in before it was caught.

Also check your unnamed antivirus for definitions updates as it could be doing a false positive.