Here's my experience:
In my copy of Firefox, I have:
* 54 .xpi files (Add-ons) of which 7 are disabled;
* 1 theme (Chromifox Basic);
* 21 plugins, of which 10 are disabled: including QuickTime; RealPlayer; all the M/soft ones - DRM-related, Media Player-related, DivX-related.
Using MrTech, I override some of the add-ons that Firefox says are "not suited to this version of Firefox". On a couple of occasions, that has caused Firefox to not start/load without instantly crashing, so I sort that out by deleting the offending add-on .xpi files causing the crash. (All my add-ons are backed up by the FEBE add-on, so I could always recover the old disabled add-on if I ever needed to)
I installed the M/soft update (I had to search for it to find it) that was supposed to make a "Disable" button on the Windows Presentation Foundation plugin, but it did not make the button, so I searched and removed all traces of WPF using a combination of RevoUninstaller, CCleaner and RegCleaner.
When Mozilla unilaterally blocked/removed the .NET plugins, I had no issue with that as I had already disabled them.
On another post in this foum ("Re: Windows Security Essentials" at:https://www.donation....msg181376#msg181376
- I referred to MSE (M/soft's virus checker program) as removing "potentially harmful or unwanted programs". To my mind, "unwanted" could include Adware, M/soft Windows Genuine Advantage and all those annoying and unnecessary plugins (e.g., DRM and Windows Media Player plugins) that M/soft has been quietly forcing into Firefox without telling you, every time you run Windows Update. One of those plugins Mozilla now blocks as it introduces a security risk and destabilises Firefox performance.
I mentioned in that post that:
* I generally mistrust M/soft as they are a perfect example of a corporate psychopath (per the film "The Corporation") and I therefore use their software with well-advised caution. I try to control that software by, for example, stopping it from "phoning home" in ZoneAlarm.
* When you see how M/soft have forced those Firefox plugins on you, it speaks volumes about their motivation and shows their deliberate intention to put their needs/desires first and their often crass disregard for the needs of the customer/victim.