On My Board (vB37x) FireFox and Google Chrome Work Fine with Quick Replies and Normal Replies.

(I've Tested with 2 Users on my Computer with 2 Browsers Opened, FireFox and Google Chrome).
This Last Version has the Problem with Old Posts Hiding After X Posts, which I Described in one of my Posts on this Thread (or the vB37x Version).
I Think that Perhaps you're Describing One of the Following 2 Problems:
1. The Bug I Mentioned with the Hiding of Old Posts, because the Posts Aren't Shown on the User's Window but they Do on the Other User's Browsers; that After X Posts, as I Documented on one Post with some Tests I Made.
2. If you have the DoublePost Prevention, and You Haven't Applied the Solution Provided by
Coders Shack to that Problem, it happens Exactly as You Described, because the Double Posts Merge but have the Conflict with this Mod in the Display of the Post Edit, which is Solved 100% with
Coders Shack Solution and Displays Great the Post Edits.
If None of the Ones Before, perhaps could be a Conflict with Other Mod, you'll have to Disable them One By One until you Find the Conflicting Mod. Once You Find It Please Post the Conflict Here for All of Us to Know and If Possible Propose a Solution.
Also, Perhaps on the New Update that
Coders Shack Mentioned for Version 1.07b, the Improvements on the Code would Solve the Problem You Mention, as Perhaps some of the Conflicts with other Mods will be Solved. We Have to Wait and Test the New Update.
My Best Regards.