CPU usage spikes when using post-editor

[Twin Volition]

As of the recent fix for whatever was causing the MM forum pages to load slowly, our computer has been getting CPU usage spikes when inside the post-editor. Sometimes it is serious enough to cause input lag when typing, and I can tell it's not being caused by anything else, as it occurs when MM is the only tab/window open, and the task manager clearly shows that Firefox (the web browser) is the only process that's hogging the CPU.

Two things particularly strange about this issue:
- Minimizing the Firefox window drops the CPU usage back to normal levels. After doing this, the issue normally doesn't return for several minutes or until making a new post
- The computer has a quad-core CPU, and yet the browser is only causing usage spikes on one of the cores (as shown in the graph)

I highly doubt this is an issue with MM's post editor (it's more likely that Mozilla just needs to fix their browser, considering their history with things like RAM-hogging), but I advise that people look into this if other people encounter the problem, and especially if it still happens when they're not using Firefox.

- Arlen