There is a way I used for a while which simply meant keeping a compressed version on hand to use after one of those auto updates.
But as I remember the real fix is deleting some file in Firefox. I do not remember what it was, but I think the fix is posted somewhere on the Firefox site - Troubleshooting perhaps?
What was happening to me with v25 or so was flash vids stopped working.
After the fix all is well and am on v27.01. It can become a security issue unless you keep current.
The idea of someone else having control over my software is very unnerving. I also just found out that Amazon Kindle for PC software has been replaced with a "cloud viewer." I don't want anything I own in a "cloud" of any sort. So I deleted the software and told Amazon I will no longer order ebooks from them until they change it back.
I'm happy with FF 24 & 25. I don't want to go any further. If they continue to change things I will indeed go to another browser and say goodbye to FF for good.