That is so irrelevant I'm having a hard time understanding why you're even bringing it up:
1. The flash plugin is honestly a piece of crap. Has always been. If running "a flash interpreter in javascript" is bad on your hardware, the plugin will be just as bad.
2. Nobody cares about performance on low hardware in the context of a project that is meant to move you off Flash and into more standard/open technologies.
3. We're talking about archival here. Performance isn't a concern today, and it definitely won't be in 70 years.
1: No, it is faster. 2: Don't make up facts. Also, if the pdf renderer will be faster and less memory intensive this will be a win for who can't afford new hardware. 3: Performance is a concern today and it definitely will be in 70 or more years. Remember, pdf part has nothing to do with archival.
You're bending facts and using rhetoric to make a false argument that implementing browser parts in C++ is somehow bad for web. These are the internal implementations of the given features and the more efficient the better.
You have got to be kidding me. You're seriously arguing that a closed flash plugin is better for archival than an open-tech-based solution because of performance?
When one requires a specific browser, with specific APIs whereas the other is a generic open source runtime?
This is a strawman, as it has nothing to do with the performance issues I brought up against your words. Though I admit I didn't know if pepper stuff was closed-source, my intuition was that it were open source if not why Mozilla would consider using it, but I was apparently wrong on that.
Still, though, that does not mean a JS pdf reader and more importantly a JS flash player are the way to go. That if you don't want to cater only to those who can afford high-end devices, which Mozilla seemingly is not doing, seen with the target market of Firefox OS and with their motto:
> Hi. We’re Mozilla, the proudly non-profit champions of the Internet, helping to keep it healthy, open and accessible to all. [https://www.mozilla.org/en-US]
