That's a hard question to answer, as Google Maps is a very complex application which uses cutting ed

That's a hard question to answer, as Google Maps is a very complex application which uses cutting edge scripting techniques. (Probably why it seems to get slower and slower, but I digress...)

Could you try disabling Firefox from using hardware acceleration? On Windows, that can be found here:

"3-bar" menu button (or Tools menu) > Options > Advanced

On the "General" mini-tab, uncheck the box for "Use hardware acceleration when available"

This takes effect the next time you exit Firefox and start it up again. Any improvement?

Since hardware acceleration improves the appearance of fonts and animations, you may want to check your computer manufacturer's website to see whether any graphics card/chipset driver updates are available for your system.