What version of Windows are you running, if you are indeed running Windows?
Oh, and if Firefox is your browser, then I will restate - reinstall Flash! andor try the same thing in Internet Explorer and see if it crashes in a similiar way, or works fine.
I do not believe your machine to be too weak for looking at and playing with web sites. It may take longer to boot up and load windows andor your browser than a newer machine, but once you are at your website, it should be only marginally slower than a rip-roaring, bought yesterday PC. Other programs may be running that are not visible to you which may be sucking some power away from you though, such as antivirus progs or instant messengers or whatever is sitting in your task bar by the clock. Undesirable programs like adware or virus(es? never too sure of the plural, virii?) can use all of your pc, not even letting you do anything you want, or certainly far more slowly than you think it should be able too.
The more recent the Operating System, the more it 'tries to do for you' so has more 'helper' programs running, so more ram and more cpu horsepower is required until you turn things that you do not use off.
Running some versions of Linux on your machine would positively fly at exactly the same task...they would be less 'pretty' than modern versions of Windows or MacOS, but would respond to your instructions far more quickly. Saying that, they would offer most users less familiarity and would therefore require more 'learning'.
Before I get into Windows bashing, Go 'Reinstall Flash' and also try the site in Internet Explorer to see if there is a common them to your freezes.