The cursor is not at the location where editing takes place

After following the proposed upgarade to V. 1.0.5. we encontered the following issue:

When I try to place the cursor on a certain line and want to enter Text, two unusual things happen:

1. The cursor is misplaced between lines
2. editing occurs one line below where the cursor is positioned

We are using Firefox V 16.0.2 and Confluence in version 4.3.2

Regards
Peter