More often than not, I have boatloads of tabs open in FireFox. Doesn't take me long to get to 200+ open tabs...
For FireFox there are extensions that can help:
Tab Manager Plus
Both can store sets of open tabs, for future reference.
Pretty certain these are available for Chrome too. But Chrome or Chrome-derived browsers will not be installed or used on any of my personal rigs. It's already bad enough I have to tolerate it on my phone.
On my lazy days I close the browser in my computers using Windows Task Manager or the infinitely better Process Explorer. This leaves the tabs intact and as browsers do a thing called 'lazy loading' of content in tabs, closing and re-opening browsers is hardly an issue. 'Lazy loading' means loading content when the tab is actually selected and not before.
My most extreme session (according to Tabs Aside): 343 tabs