I would like to get some input on browser speeds in regards to JS/ExtJS.
In the beginning I used FF 3.6/Linux to develop my app due to Firebug. The speed was OK, but a bit slow in rendering forms. (3~5 seconds). IE is slower yet. (Yes ... this is with Firebug disabled)
I then decided to install Chromium and the forms load instantly. The entire application is more responsive. Almost to the level of a regular app.
I've started using Chrome (with the build-in developer tools) too, but I do miss some Firebug features, so I still switch back sometimes.
Firefox is partly slower because of the way Ext layouts are programmed. The way they use style information is not optimized for Gecko. This will be a lot faster in Ext 4.
For IE 6 and 7: Use quirks mode (no DOCTYPE). Ext layouts have to work a lot harder in strict mode.