Why not have them all for practicality, learning and just plain fun. I have IE9, FF, Slimbrowser, Chrome and Opera all on this system. FF is the main browser while all the rest I just tinker with. No conflicts at all.

DA

Every browser is just a little bit different from the other, and how useful that is to you depends on how much you're willing to learn and how much time you want to invest. I use FF by choice, IE for work because I have to, and I keep Opera on hand just in case. On my computer Opera is kept updated but otherwise unused so if worst comes to worst a fully functional and uncorrupted Opera is there ready to help save the day. That works for me, YMMV.

Thanks for the comments. :-)

Yes, I myself do have several non-IE browsers (FF, Opera, Comodo Dragon [Chromium]), but the relative I mentioned only has FF at this point (besides IE which she doesn't like at all). She was thinking that for a back-up she'd like to just have SM, since its interface is very similar to what she's used to with FF.

But she is concerned that if something happens that would 'crash' FF and make it unusable (requiring another browser to "save the day," as azinoh nicely puts it) might end up being something that also affects SM, because they're so close. IOW, she'd prefer having SM but only if it's 'independent' enough (as Opera and Chrome would be) to be there for her if FF isn't. From the comments above, I'm assuming that she can safely install SM (and only SM at this point) and consider it her secondary browser -- with IE a distant third. :-)

I use Sea Monkey as my default browser and I also have Firefox and IE on this computer. You can use both with out any problem.