Firefox often slow, not responding and showing unresponsive script errors.

Question

In the last few weeks, firefox has often gone unresponsive, usually shown as 'not responding.' This lasts anywhere from a few seconds to several minutes (possibly longer, but by that amount of time I loose patience and 'end task' in task manager.) This is usually followed by an 'unresponsive script' error. Which script it is varies. I've been responding by clicking 'stop script,' which usually fixes the problem temporarily.
The problem seems to occur mostly randomly, but will predictably always occur on site with videos like youtube. Here it is also worse, taking much longer to resolve if it does at all. I've got flashblock active, and sometimes the error will occur before I get a chance to activate the video and sometimes after, but will always occur. Also, on this sort of site, the 'unresponsive script' error will also go unresponsive most of the time, which I've not seen anywhere else, meaning that the only solution, after a while is to end the process in task manager. I've at times attempted to play the same video for half an hour with no success.
As I've therefore spent a fair bit of time in task manager, I've noticed that I end up with many processes running for FlashPlayerPlugin_15_0_0_152.exe*32 (Description: Adobe Flash Player 15.0 r0.) They build up the more I use firefox, but go away when I restart my computer. I've gotten up to at least 50 at one point. Most use 128 or 124 K of memory, but about 1 in 7 uses between 1-5000 K. I don't know if this is linked to the above issues, but I've only noticed it since it started.
I've tried resetting firefox and it changed none of the above.
If it helps, I used Windows 7. Feel free to ask for any more details about my system and I will do my best to answer, though I'm not an expert in computers. Thank you very much in advance for your help.

Answer 1

Thanks for the advice. What solved it was disabling all addons and then restarting the computer. I've since reenabled Adblock (2.6.4) and Flashblock (1.5.17) without causing the problem to reemerge, leaving Troubleshooter (1.1a) as my only previously enabled addon I've not reenabled. I am no longer experiencing the issue.
Regarding updating to version 32, I tried this, but the official site told me I already had the most up to date version of firefox for some reason. Normally, it updates automatically. However, as my issue has been solved I don't consider this a problem.
Thank you very much for your advice.