I use Firefox as my main browser (and always have -- just to give some context about where I'm coming from). But Firefox's developer tools are just not as good as Chrome's. Again, I use Firefox. But every couple months or so, I stumble upon some annoying instance where its developer tools are either inadequate or are just buggy (whether it's the element inspector not working, or pausing on a debugger statement and not giving me a source view, or applied CSS rules not showing up, or some weird behavior in the console, or...), and I have to resort to using Chrome's developer tools to get the issue resolved. This easily accounts for 90+% of my Chrome usage (i.e. more than the number of times I've had to resort to opening a website in Chrome because the developers didn't test it in Firefox).

Have you used the firefox performance timeline, it is awful. Chrome's performance timeline is amazingly smooth and has much more features.