Using Safari on an iMac with a 4Ghz i7 chip and 32GB RAM. Should be enough horsepower I would think?
Yes @Geektastic - I agree.
I just gave it a try by logging in on the Macbook Pro using Safari. It froze - the same as you report - when trying to load the base 64 image in the edit window. And it well and truly froze - killed it after a minute or so, then
double-checked by logging in on the same Macbook using chrome - it worked no problems.
So unless there's a huge coincidence, there seems to be a particular issue with using the "quote" function when there's an embedded base 64 image in the post, when using Safari on a Mac. Perhaps start a thread on another forum (Geekzone?) - it's a bit off-topic here.