I use Firefox to read the news. I have it on a schedule, so it opens up a half hour before I get up, so by the time I'm at my computer, they are all loaded & waiting.
Before the last update, all the tabs would reload on start-up. Now, several sites don't. I assume they are reloading from the cache, since the page is identical to the page the day before. Hitting the refresh button will solve the problem, of course, but then I have to wait for the page to reload. Not the end of the world, but a little inconvenient.
Some browsers have an option to force the browser to ignore the cache, or to delete the cache when the program quits, but I've not found a way to do either one in Firefox.
I don't think that there is an (easy) way to achieve this.
Current Firefox version appear load pages from the cache on startup and the only way to avoid this would be to clear the cache when you exit Firefox, but Firefox won't use the disk cache at all in that case as you can see in about:cache.
The browser.cache.check_doc_frequency pref doesn't have effect as well on the startup and even reload all tabs isn't always working for me the first time and I may have to reload all tabs a second time.