The systems I use on a daily basis are fairly unusual.
My platform at work is unusual insofar as it isn't Windows, Mac or Linux: it's Solaris. It's not that unusual in the commercial world (thank goodness we've retired almost all our Solaris/x86 boxes - now that is unusual), but no one casually using their Gatesware PC at home will have heard of it. This means, apparently, that it doesn't matter if the respective owners of Flashplayer and RealPlayer don't release up-to-date versions for it (and you can forget any player capable of playing either Shockwave or Microsoft's proprietory multimedia streams). However, because it isn't that unusual, you can at least get a moderately recent version of Netscape, Java 1.4 (which was after all invented by Sun), Acrobat Reader, etc.
The system I use at home is unusual because it's a version of Red Hat Linux which was in vogue about five years ago when I first installed it. It's not going to get upgraded because it runs (relatively) fine as it is and it hasn't got the disk space or cpu/memory to run Red Hat's latest bloatware - and besides, I thought I'd bought myself a new(er) laptop to upgrade into until it got appropriated by my other half <g> [no distribution wars please - yes I'll probably have a Debian machine of some sort eventually, but now is not the time]. The main problem with it is glibc-2.0.7 which no one uses any more, so pre-compiled binaries never work.
So: no version of Netscape later than 4.74 will work; yes RealPlayer 7 will work, but 8 won't; Flash 5 will work (with Netscape 4) but 6 won't, and the latest version of Java which still works is 1.1.x (certainly for x=6, not sure about others). Acrobat 5 does work, for some reason.
This is one reason why I like plain HTML web pages without stupid gimmicks on them.
But wait: Mozilla 1.3 does work! Why? Because it's open source, and relatively straightforward to compile (given 8 hours or so and an NFS server to plonk the huge build directory on), though it does need a small hack for glibc-2.0. Of course, it now won't co-operate with the Flash or PDF plugins, and it requires Java >=1.3 because it doesn't have its own Java VM, so that's out too. See - open source good, closed source bad.
Must get around to compiling Mozilla 1.4 (or 1.5 if it's out by the time I get around to it).