Sure there is. A while ago, while I was using the 4.0 beta, I ran into a problem: modal dialogs wouldn't work. In beta 4 they worked just fine. Beta 5, just fine. When beat 6 rolled around, they stopped working. I reverted and used that until beta 12 fixed my problem. 6-11 were useless for some of the things I used it for (example: TiddlyWiki editing) because Javascript alert() and confirm() dialogs would literally not show up.
EDIT: also, the bash script is there because I install Firefox to /usr/local, and it's easier to type "update-firefox" in an already-open terminal than to reboot Firefox as root so it can modify my files. I'm aware it's redundant, but it also a) requires my active participation, so I can't miss it and b) lets me downgrade, in case of something like what happened above.
EDIT: also, the bash script is there because I install Firefox to /usr/local, and it's easier to type "update-firefox" in an already-open terminal than to reboot Firefox as root so it can modify my files. I'm aware it's redundant, but it also a) requires my active participation, so I can't miss it and b) lets me downgrade, in case of something like what happened above.