If you are using a Master Password and also have Firefox Sync enabled, you will be asked for the password every time you open Firefox. This is because Firefox cannot connect to the Firefox Sync services without the Master Password entered. Since Firefox will immediately attempt to connect to Firefox Sync services when you first open Firefox, you will get the password prompt.

For more information, please refer to Using a Primary Password with Sync.

Another possible cause of the MP prompt at startup can be the hotfix extension to add the new intermediate certificate to the Firefox Certificate Manager. If you have this extension listed on the about:studies page then try to remove it when possible.

If you run Firefox 66.0.5 then you no longer need an extension or other workarounds to install the new certificate, so possibly also check the about:addons page.

• https://support.mozilla.org/en-US/kb/update-firefox-latest-version

In addition to cor-el's post :

In case this isn't due to having a Firefox account (see Wesley Branton's post) and you didn't participate in the Firefox studies, then maybe you could check to see if there is a "hotfix" related extension in 3-bar menu => Add-ons => Extensions.

If you're extensions are (no longer) disabled (if you had any to begin with) then the hotfix extensions can be removed.

Thank you all for your input. And thanks mostly to Cor-el. That "hotfix-update-xpi-signing-intermediate-bug-v1.0.3-1548973" thing you referred to was indeed active. I disabled it and the password nuisance prompt is now gone.

Is that something I need? My other PCs have that 'study' also, but not active. It is marked complete.

Is Mozilla is using my machine in the background for 'studies' on how I use my machine w/o my knowledge?

Hi Clutch, Studies let you try out different features and ideas before they are released to all Firefox users. They are 100% transparent and you can opt out of individual studies or all studies altogether. You can see more in your: Settings Privacy & Security Firefox Data Collection and Use

As the user above already mentioned, Firefox Studies is for testing experimental features. You can opt out, if you wish. More information about Studies can be found in the About Studies document.

In this specific situation, the hotfix-update-xpi-signing-intermediate-bug-v1.0.3-1548973 study was a temporary fix for a widespread issue with add-ons in Firefox. If you have updated to the latest version of Firefox, that study should not be required. More information on the issue and how Mozilla fixed it can found in the Add-ons disabled or fail to install on Firefox document.