Regarding speed: it's not that Firefox got slower, it's that Chrome set a new performance bar that Firefox had to meet --- and largely has met! Though a cost of meeting that performance bar was dropping XUL extensions, which is one of those changes that people still complain about.
Contribution to Mozilla's defeat of IE is one of the great accomplishments of my life, but having been there for both fights, the fight against Chrome definitely was much tougher. Microsoft took their eye off the ball and basically stopped working on IE for a few years, which gave Mozilla a huge opportunity; no such luck with Chrome. The complexity of Web sites has increased a lot which makes it much harder to keep up and surpass a more well-resourced browser.
Contribution to Mozilla's defeat of IE is one of the great accomplishments of my life, but having been there for both fights, the fight against Chrome definitely was much tougher. Microsoft took their eye off the ball and basically stopped working on IE for a few years, which gave Mozilla a huge opportunity; no such luck with Chrome. The complexity of Web sites has increased a lot which makes it much harder to keep up and surpass a more well-resourced browser.