Firefox had been underperforming during part of its life, but deep internal improvements meant those days are over. There is a huge difference in memory and CPU usage between older Firefox and the one we have today. Sadly, lots of people still think that Firefox never changed.
I did a quick memory usage test, just for having my personal anecdote and some numbers to show. The result was that Firefox uses an average of 10 MiB for each open (and active) tab. Not bad at all!
First, what I'm testing:
* Firefox 115, on Linux Mint 20.3 (which essentially is Ubuntu 20.04).
* 13 extensions installed. Some are uBlock Origin, Amazon Unsponsor, Bookmark Search Plus, DeArrow, Multi-Account Containers, Keepa, One-Click Wayback, Tree Style Tab (guys try this one out for a great vertical tab tree!).
* 90 tabs open. Tree Style Tab makes me open lots of tabs, because it is then so convenient to open/close subtrees for different topics... but I digress.
* Tabs include: 4 videogame stores, which are heavy on graphics and dynamic content. 10 shopping tabs in various shops, including Amazon. 10 YouTube videos (buffering preloaded). 14 Google Drive / Google Docs tabs (heavy on JS usage). Various documentation pages, and too many HN threads to admit.
* Firefox configured to remember all tabs when closed, and restore them when opening. Upon firstly starting, Firefox doesn't actually load the tabs. They are in suspended, inactive state, until opened for the first time.
RAM usage results:
* Cleanly started, only HN frontpage loaded: 372 MiB.
* HN frontpage and this entry opened in tabs: 386 MiB.
* Third HN tab opened: 394 MiB.
* Went through ALL 90 tabs to force them loading: 954 MiB.
Conclusion: Firefox uses around 10 MiB per loaded tab.
Screenshots of Btop++:
* In the middle of loading all 90 tabs. CPU is busy! https://pasteboard.co/Bxf2TI9P8YT2.png
* After all tabs have been successfully loaded. Resource usage is back to being stationary. https://pasteboard.co/m3tVzYNMtDmD.png
(The reason for this post is all those comments here and in other entries, claiming that Firefox was a resource hog for them a while ago, and that's why they nowadays are committed Chrome users. In light of recent events, we really need to collectively reduce Chrome usage numbers!)