All Mangas Reader

You're right, it definately would add up, and it's a good idea, but I think Polo is gonna be saving it as webSQL data in up and coming versions.

Any other ideas to decrease the amount of characters in the stored data that we can use until then?

Stripping the word 'chapter' from variable names. That would save 14 characters per mirror. Stripping Read from them would save 8 more (but make it harder to read), but on the other hand you can remove the 'ast' from the variable names with last and it would still be readable and save you 6 characters per mirror.

...and storing the data into a nodular format like XML would technically reduce the size a good deal as well, as seen by my edited post above.

EDIT: Added the blue text

Even further, you can strip the 'http://' from the host name to save another 7 characters per manga, then add it in programatically later.