@wkerby: Not sure if this will help: there is a Firefox add-on called Auto Copy 1.0.1 which does this, except it should copy automatically regardless of whether CHS is enabled.
If "Firefox is getting buggy" then it may be that you have some bad or conflicting add-ons.
I say this because Firefox otherwise is generally stable as anything - even the latest ß versions, which I run all the time.
I use a lot of add-ons and Greasemonkey scripts, and the only time I get any problems is when one of them starts to play up (usually because Firefox has been updated!).
By the way, Auto Copy works fine for me (I use CHS also).