Something similar is annoying me as well.

- OSX 10.10.2 (Yosemite latest)
- Firefox 35.0.1 (latest for the moment)
- Firebug 2.0.8 (but it seems that doesn't matter if installed)

I'm using Sencha CMD to develop (easier for me to build the production packages), but I do NOT watch for app changes, as the rebuild of the development packages is needed only when I change something in SASS or add some overrides.

If I refresh the app, very often the layout is not rendered correctly:

- main tab panel header height is lower;
- missing lots of titles (for all windows anyway)
- close (action) icons are misplaced (on the left, on top of each other)
- strange dimensions for windows
- if I collapse east side menu panel everything is blue (nothing else visible)

and so on...

It seems some sort of CSS not applied, applied incorrectly or not at the right time...

The app works (almost) fine, if I resize window a little bit the height of the main tabpanel header corrects itself, but still missing titles, wrong window action icons placement.

It was driving me crazy as I had to refresh couple of times until I got it once working, as on Windows machine works just fine for every refresh.

I have web developers toolbar add-on installed as well, with disable cache option checked.
I've also disabled browser's cache in about:config like I did on windows as well.

Usually I stay on Console tab in Firebug.
But accidentally have seen that if on Net or Script tabs, it works on each refresh !!

- disabled firebug, restarted FF, same issues
- disabled all add-ons, restarted FF, same issues
- removed firebug, restarted FF, same issues (so clearly it's not a Firebug bug)
- opened FF developer internal tools, refreshed, and it was working fine
- checked options of tools, and the option to disable cache when tools panel opened was NOT checked, I've checked it (but disabled entirely in about:config anyway)
- reinstalled Firebug
- having FF dev tools opened and Firebug on Console tab, works as well

So now I keep opened internal FF dev tools panel opened (undocked, somewhere behind) in order to use Firebug in good conditions.... but it's NOT Firebug bug !

Edit: This is not perfect neither, but the issues are a lot more rare now !