WHAT IS AN ODEX FILE?
In Android file system, applications and framework files come in packages with the extension k@. apk or .jar. These APKs or JARs contain certain .odex files whose supposed function is to save space. These ‘odex’ files are actually collections of parts of an application that are optimized before booting. Doing so speeds up the boot process, as it preloads part of an application. On the other hand, it also makes hacking those applications difficult because a part of the coding has already been extracted to another location before execution.
THEN COMES DEODEX
Deodexing is basically repackaging of these APKs or JARs in a certain way, such that the .odex files are reassembled into classes.dex files directly integrated inside the APKs or JARs. By doing that, all pieces of an application package are put together back in one place.
For now, we need Baksmali.jar and Smali.jar to deodex, it seems these tools are not perfect and it seems to be why deodexed stock browser is laging/freezing.
This is the reason why there is a return to odexed customROMs