App Tabs aren't saving after exiting Firefox and "Restore Previous Session" doesn't exist anymore?

I'm having this problem with Firefox and it just started today. I always have my App Tabs set on the left side of the tab bar, and usually, when I exit the browser, those 3 App Tabs are always there with my home page for me when I start a new session. But today, when I close the browser with the 3 App Tabs there, they disappear and only my home page appears when I start a new session. Also, I see that the "Restore Previous Session" option in the History section is greyed out, so I can't use that anymore. What's going on there? I cleared my recent history (everything) yesterday and I check-marked all the options to delete for the history, so was that my mistake? Thanks in advance!