Yes, Firefox can be a resource hog. Each time you open a tab it takes more and more resources to simultaneously run those tabs, with the amount of resources being consumed depending on the site and the amount/type of content ran on each site, within each tab.
I just did a test myself and with Firefox open and sitting on Google it takes up roughly 120MB of memory. Once I opened a few tabs, those being Tom's Hardware, ESPN, Facebook and Youtube, it went from the initial 120MB to over a little over 300MB being used. If I continued, more memory and resources would be demanded and the computer would get slower and slower.
If she has 15-30 tabs opened, there's a good chance her computer is going to stall and not run properly, if at all. It all depends on how powerful her computer is and what kind of sites she's going to. If she has 20 Google pages open, it's really not a big deal. But if she has a bunch of media intensive pages open, it's going to give you problems.
The speed of the CPU, the amount of memory she has (RAM, not harddrive space), and other programs she's also running has a huge influence as to how many tabs she can run at the same time.
I'm not sure why though she feels the need to have so many tabs open if she can only view one at a time? That's like complaining that your Jetta doesn't go that fast because you have 10,000 lbs of metal in the trunk. Lol. Maybe she needs to start utilizing bookmarks/favorites...
I hope this clears things up for the both of you!
