This bug only happens with firefox. Tested on versions 14 and 15 beta.
The behavior cannot be replicated on IE or Chrome.

When adding a new row on a table with a lot of content (500x4), firefox gets slow and shows the following Javascript error:

A script on this page may be busy, or it may have stopped responding. You can stop the script now, or you can continue to see if the script will complete.

Script: https://127.0.0.1:8444/confluence/s/en_GB/3281/20/e057e0bc4cec8ae164a31b164cb12cff/_/download/contextbatch/js/editor,macro-browser/batch.js:95 

After clicking on Continue two times, the row is been added.

A workaround is to increase the time on dom.max_script_run_time property on Firefox. However this workaround just avoid the error to be shown but the delay will continue.