My reply was based on your statement:
+"I deleted the files that allow Firefox to use quicktime *as a plugin."*+
No mentioned of +streaming videos.+ For streaming videos, Flip4Mac browser plug-in is mapped to play those in my version of FireFox.
If you have not already done so, download the following:
RealPlayer
Flip4Mac
VLC Media Player
Perian (AVI and FLV support)
Adobe Flash Player Software
After the installation(s) make sure you repair permissions and restart your computer.
If you can post a link of the streaming video you are trying to watch, we can check it out & possibly advise you which "player" in combination w/QT you need to watch it with. This way you can map it w/FF if need be.