Why is YouTube on Firefox so unbelieveably slow, slower than on iPhone?

I have tried clearing history, cookies and cache, then restarted firefox. I still can load videos faster on YouTube using my iPhone 4s using the same Wi-Fi that my laptop is using for Firefox and they load in seconds. On Firefox it doesn't even load a third of the way and I've already watched a 5 minutes video twice on my phone.

What can I do to make Firefox load Youtube videos faster? Their help page was no help, told me nothing that made it better and offered only really stupid suggestions to be honest.

Added (1). I went to add-ons but there's no update feature. I'm super confused, when did this get so complicated…

Added (2). Updated Adobe Flash Player. And now it's even slower, more choppy and now the sound is becoming affected. This sucks. My internet connection is very fast.something is wrong with the browser.

Added (3). I ran the two commands. No effect still choppy as hell and sound is still affected. I try to let the whole video load, but once I go back to the starting point (I have to "chase" the grey bar to make it load, then bring it back to the beginning to start the video from the beginning) it just all goes away like it didn't load anything. Then it's choppy and keeps trying to reload it over again.

Added (4). 13 add-ons I disabled the old Shockwave version it's still there for some reason.

Added (5). No I didn't.

I tried lowering the quality of video… No help. Disabling the older version of Shockwave, believe it or not, made the choppiness worse.

Added (6). Restarting computer didn't help.

It doesn't tell me what's outdated or not on the addon page.

Added (7). Clicked on link where it checks for out of date add ons. Flash is up to date. Playback still choppy.

Added (8). Firefox 14.0.1 just updated not very long ago, and I can't remember having this problem with YouTube before the update.

Have you updated you add-ons in firefox? Sometimes this helps
*tools
*addons (bring you to plug-ins page)
*check to see if add-ons updated. This will open a sepearte browser page, if any add-ons are outdated follow the instructions and update them. Hope that helps? Cheers
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:-)

ps.:
After add-ons updated should run 2 commands through cmd window

ipconfig/flushdns
netsh winsock reset

This may cause your browser to slow down when 1st loaded initially but once the cache is updated then the 2nd time should be little faster

ps: The update link is almost at the top of the page. It says (or should say) "check to see if your plugins are up to date" It is just a sentense that you have to left click on.

Further: Okay on your add-ons page, how many add-ons do you have listed there?

more: :) just a question, when you updated adobe flash player did you close your Firefox Web browser while it was installing?

*** go back to the addon pages and choose check to see if addons updated again. Once you are on the adobe flash player page, choose download. When prompted choose run the file. Then close out your firefox and wait for the update to complete. I think you will notice on the add-on page that adobe flash player is still outdated. Try that.

*** okie another try, what version of Firefox do you have? Click on Help Menu (in Firefox) Then choose "about". If firefox 14.x then there maybe a newer version.

*** There's a Firefox 15.x out now try downloading that. Just a question about youtube. Are you watching the videos in HD. Cuz I had to reduce my Youtube quality from HD to 360p.

^&^&^& Did you try downloading the newest firefox? The age of computers is frustrating lol. Did you try reducing the Video quality from HD to 360p within youtube?