Currently, if I want to only add one or remove one extension in my local firefox build, I have to load browser/config/mozconfig and copy the long line and paste it in my editor and then make my changes. I should be able to define a variable in my .mozconfig which gets picked up.

Like such. In my .mozconfig, I then will add: ac_add_extensions --enable-extensions=$FIREFOX_DEFAULT_EXTENSIONS,layout-debug

Alternate approach: In my .mozconfig, I will add: ADDITIONAL_FIREFOX_EXTENSIONS=,layout-debug with the caveat that this must be done prior to the ". $topsrcdir/browser/config/mozconfig" line. Dauphin prefers this method, but I much prefer the previous method. I don't care too much, really. Just so long as one of these methods get done. Someone will need to write a similar patch for thunderbird (there are a few other things which could get customized there and probably should be, but I won't bother since I'm not sure which approach you like best)

I lean to #1 because of a theoretical consideration: . $topsrcdir/browser/config/mozconfig . $topsrcdir/mail/config/mozconfig . $topsrcdir/calendar/config/mozconfig ac_add_extensions --enable- extensions=$FIREFOX_DEFAULT_EXTENSIONS,$THUNDERBIRD_DEFAULT_EXTENSIONS,$SUNBIRD_ DEFAULT_EXTENSIONS,layout-debug