regarding ur first problem as i understand. if ur using GUI KDE the right click on the bottom panel of ur window and click the configuration option. while selecting layout option at the top left of that window select last of the tab(i dont really remember its name). there u will select the menu or sub menu u want to add fire fox to(most probably internet). the add new item. by doing this u will get a new dialog.in this dialog u r to specify the path of the command which u want to execute for that button press. more over there is a mension for the icon once u click it u get an exaustive list of icon, both system and user, there u can select fire fox icon with fire surrounding a fox. i have seen it there.
and now for ur second problem u can use Mplayer. it will play all ur videos and audios.its really easy to install with all the process listed in the site. all u have to do is to get three things.
mplayer main binaries
a font(u can have more fonts but only one will also do)
a skin(u can have more skins but only one will also do)
the site where u can get all these is
one u have got all those file u will note one thing. some file r with extension
.tar.tar and some with tar.bz2. to unpack these archives use the following commands
tar jxvf package-name
tar xvf changed-package-name
and then all that ./configure and make steps
only first step is different
rest all is the same as in the case above
i hope that u get it installed cleanly but if dont feel free to ask.