''OptimizerMonitor.dll'' is a malware application. Perform a full scan with an AV along with Malwarebytes and refresh Firefox, based on the below directions. If Malwarebytes kicks in every now and then, it means you didn't totally get rid of the malware. If the same malware keeps popping up, I'd recommend to re-install your system from scratch. Hello, The Refresh feature (called "Reset" in older Firefox versions) can fix many issues by restoring Firefox to its factory default state while saving your bookmarks, history, passwords, cookies, and other essential information. '''''Note:''' When you use this feature, you will lose any extensions, toolbar customizations, and some preferences.'' See the [[Refresh Firefox - reset add-ons and settings]] article for more information. To Refresh Firefox: # Open the Troubleshooting Information page using one of these methods: #*Click the menu button [[Image:New Fx Menu]], click help [[Image:Help-29]] and select ''Troubleshooting Information''. A new tab containing your troubleshooting information should open. #*If you're unable to access the Help menu, type '''about:support''' in your address bar to bring up the Troubleshooting Information page. #At the top right corner of the page, you should see a button that says "Refresh Firefox" ("Reset Firefox" in older Firefox versions). Click on it. #Firefox will close. After the refresh process is completed, Firefox will show a window with the information that is imported. #Click Finish and Firefox will reopen. Did this fix the problem? Please report back to us! Thank you. ________________________________________________________________________ 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 [[Profiles - Where Firefox stores your bookmarks, passwords and other user data|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. #Download the latest Desktop version of Firefox from [https://www.mozilla.org mozilla.org] (or choose the download for your operating system and language from [https://www.mozilla.org/firefox/all/ this page]) and save the setup file to your computer. #After the download finishes, close all Firefox windows (or open the Firefox menu [[Image:New Fx Menu]] and click the close button [[Image:Close 29]]). #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 [[Installing Firefox on Linux]]. If you downloaded and installed the binary package from the [http://www.mozilla.org/firefox#desktop 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 [[Troubleshoot and diagnose Firefox problems#w_5-reinstall-firefox|here]]. <b>WARNING:</b> Do not use a third party uninstaller as part of this process. Doing so could permanently delete your [[Profiles|Firefox profile]] data, including but not limited to, extensions, cache, cookies, bookmarks, personal settings and saved passwords. <u>These cannot be easily recovered unless they have been backed up to an external device!</u> See [[Back up and restore information in Firefox profiles]]. <!-- Starting in Firefox 31, the Firefox uninstaller no longer lets you remove user profile data.Ref: Bug 432017 and https://support.mozilla.org/kb/uninstall-firefox-from-your-computer/discuss/5279 [Fx31] Windows uninstaller will no longer offer the option to remove personal data --> Please report back to say if this helped you! Thank you.

Yes, reloading Firefox from the Mozilla website solved the problem for Firefox, but not for Thunderbird, so malwarebytes is still hobbling. Thank you. We are making progress. I would still like to know how it is possible for 1) a windows support program to get changed to malware 2)how it gets embedded in Mozilla software, 3) why such a program as OptimizerMonitor.dll cannot be easily displaced or substituted.

It's not unusual for malware to get disguised as Windows components. That often happens with ''svchost.exe'', for example. A virus injects its code into a DLL or an executable and that's how it replicates, that's why it's called "virus". If such a file results to be a system file, that's not easy to remove, because it's locked by the operating system. I'd suggest to go to Safe Mode and check for the integrity of your system files by running the '''SFC /scannow''' command.