/When/ they went, which, iirc was Netscape 4 (?). It was horrendous, crashing, slow buggy, awfulness, which the previous version really wasn't. This was when it was all closed and proprietary.
Firefox came a long time later. Well after Mozilla opened.
No idea if Firefox would be better if they'd stayed in c. What i do know is that c++ is a vastly, vastly better language now through no fault of the standards committee. G++ got good. Then came clang++, valgrind was an amazing leap forward too.
Before all that there really was no such thing as cross platform c++.
when they went to c++ it became Firefox. do you think we'd have a better firefox today had it stayed in C ?