The path towards deterministic builds is definitely not clear. As many in this thread have pointed out, it's a difficult technical problem. The difficulties are multiplied by a project at Firefox's scale.
Further complicating matters is our platform breakdown. The majority of Firefox users are on Windows. Deterministic builds on Windows are very painful. And that's before you figure PGO into the mix. Tor works around this by compiling Firefox with an open source toolchain and doesn't use PGO. But that's a non-starter for us because choosing an open source toolchain over Microsoft's would result in performance degradations for our users. Believe me, if we could ship a Windows and Mac Firefox built with 100% open source to no detriment to our users, we would. There's work to get Firefox building with Clang on Windows (but only for doing ASAN and static analysis, not for shipping to users). That gets us one step closer.
All that being said, there has been exploratory talk lately of serving segments of our user base with specialized Firefox builds. e.g. a build with developer tools front and center that caters to the web development community. If that ever happens, I imagine a deterministically-built Firefox with things like Tor built in could be on the table. The way you can make that happen is to direct noise directly at the Mozilla community. Send a well-crafted email to firefox-dev (https://mail.mozilla.org/listinfo/firefox-dev) explaining your position. Anticipate that people will likely reply by asking you to prioritize this against existing goals, such as shipping 64-bit Firefox on Windows and shipping multi-process Firefox. We don't have nearly unlimited resources like some of the other browser vendors, so we can't just do everything. Again, I implore people to directly contribute to Mozilla any way they can. https://www.mozilla.org/contribute/
Further complicating matters is our platform breakdown. The majority of Firefox users are on Windows. Deterministic builds on Windows are very painful. And that's before you figure PGO into the mix. Tor works around this by compiling Firefox with an open source toolchain and doesn't use PGO. But that's a non-starter for us because choosing an open source toolchain over Microsoft's would result in performance degradations for our users. Believe me, if we could ship a Windows and Mac Firefox built with 100% open source to no detriment to our users, we would. There's work to get Firefox building with Clang on Windows (but only for doing ASAN and static analysis, not for shipping to users). That gets us one step closer.
All that being said, there has been exploratory talk lately of serving segments of our user base with specialized Firefox builds. e.g. a build with developer tools front and center that caters to the web development community. If that ever happens, I imagine a deterministically-built Firefox with things like Tor built in could be on the table. The way you can make that happen is to direct noise directly at the Mozilla community. Send a well-crafted email to firefox-dev (https://mail.mozilla.org/listinfo/firefox-dev) explaining your position. Anticipate that people will likely reply by asking you to prioritize this against existing goals, such as shipping 64-bit Firefox on Windows and shipping multi-process Firefox. We don't have nearly unlimited resources like some of the other browser vendors, so we can't just do everything. Again, I implore people to directly contribute to Mozilla any way they can. https://www.mozilla.org/contribute/