The charset issue with Ajax has been discussed in a few past threads as well. To be honest I've never really looked into it, but based on a search on Google, the solution seems to vary, from calling:
before the Ajax request is sent inside the .js file, to using scripting to do a search and replace of the offending characters.
The first suggestion might be worth a try. Inside ajaxtabs.js, make the following change (in red):
Test this out in Firefox to see if it makes a difference.