Both firefox and thunderbird fail to build with identical errors about the C compiler not working:
checking whether the C compiler (x86_64-pc-linux-gnu-gcc hBmarch=native -mno-avx -O2 -pipe -Wl,-O1 -Wl,--as-needed) works... no
The C compiler works for all the other compiles, so I expect there is no problem with it, but rather with the mozilla configurations.
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If I am reading this right, your saying only thunderbird and firefox are failing to build on your system. I have rechecked configure and only thing I can see is a hBmarch instead of -march which would point to a corrupted enviroment.
Please test with current builds. If you can still produce feel free to reopen and update bug.