We already know Firefox shows a notification to refresh (formerly known as reset) the browser if you’ve not used for 60 days, Mozilla also wants to display a similar notification to the user when he reinstalls the browser. After reinstalling Firefox (irrespective of channel –Nightly, dev, beta or stable) an infobar with refresh button, will appear at the bottom of the screen with the message: ‘Looks like you’ve reinstalled Firefox. Want us to clean it up for a fresh, like-new experience?‘ (check the screenshot below for the same for Nightly).
You can spot this change, in latest version of Nightly.
Disable Firefox’s refresh notification
FYI, the company is planning to preserve the add-ons (but disable all of them) after refresh, so reset won’t likely will remove the add-ons in future.
If you don’t want the reset notification to appear when you reinstall Firefox or don’t use it for two months, visit about:config, create a new boolean preference named browser.disableResetPrompt and select its value as true.