Making Firefox retain already-loaded web content when tablet is put to sleep

I recently got an Android tablet and loaded Firefox on it as my browser. I primarily intend to use it for reading web content, sometimes when offline - i.e., I'd like to be able to load some websites at home, leave Firefox open and put the tablet to sleep (NOT shut it off), go somewhere where I don't have wifi, then wake up the tablet and read my loaded websites - just like I could do with my laptop, but much more portably. The issue is that it seems like when I do this and go into Firefox after waking up my tablet, the browser seems to want to always reload the webpage from scratch. This is a pain both because it means I have to have wifi access to read webpages and because I'm often partway through a very long blog/forum post or something similar, and I have to spend a bunch of time scrolling back to where I was. Anyone know why this is happening and what I need to do to get Firefox to just hold on to the content I've already loaded?