I believe they do use just as much RAM as current tabs, it’s just computers are better at handling it now.
Mozilla makes reference to them eating RAM, but I’m not 100% sure.
Use fewer tabs
Each tab requires Firefox to store a web page in memory. If you frequently have more than 100 tabs open, consider using a more lightweight mechanism to keep track of pages to read and things to do, such as:
Bookmarks. Hint: “Bookmark All Tabs” will bookmark a set of tabs.
Save web pages for later with Pocket for Firefox.
To-do list applications.
In general, yes more tabs = more RAM used, but Firefox does have a neat trick compared to Chrome that helps lower memory usage for those of us with hundreds of tabs. When you launch Chrome with a bunch of tabs open from a previous session, it actually loads them all into RAM at launch, with Firefox, it doesn’t actually load the pages of tabs from previous sessions, until you switch to them. The page titles and icons get loaded into RAM, obviously, but if you have lots of old tabs that you almost never open, the memory usage impact of lots of tabs is minimized.
I believe they do use just as much RAM as current tabs, it’s just computers are better at handling it now.
Mozilla makes reference to them eating RAM, but I’m not 100% sure.
https://support.mozilla.org/en-US/kb/firefox-uses-too-much-memory-or-cpu-resources
In general, yes more tabs = more RAM used, but Firefox does have a neat trick compared to Chrome that helps lower memory usage for those of us with hundreds of tabs. When you launch Chrome with a bunch of tabs open from a previous session, it actually loads them all into RAM at launch, with Firefox, it doesn’t actually load the pages of tabs from previous sessions, until you switch to them. The page titles and icons get loaded into RAM, obviously, but if you have lots of old tabs that you almost never open, the memory usage impact of lots of tabs is minimized.