~/.mozilla/firefox/
     ***.default-release/
       storage/default/
         moz-extension+++***/  not followed by ^userContextId
           idb/
             ***.sqlite

Firefox seems to constrain the maximum size of the ".sqlite" file in "storage/default" in "~/.mozilla/firefox" to 10% of the free space of the partition containing the home directory of the user. I need to let the ".sqlite" file grow very large, even larger than the free space of the partition containing my home directory. Therefore, I need the following two points. 1. I would like to disable this 10% constraint. 2. I would like to place this ".sqlite" on an external USB drive (or USB stick) without moving the entire "~/.mozilla/firefox" directory to the external USB drive. The path of this ".sqlite" contains an enigmatic alphanumeric string and hexadecimal digits, which differ from user to user and from machine to machine, and which may be inappropriate to be exposed to the public. So, I refrain from showing the exact path. Instead, I will describe the path. The directory "~/.mozilla/firefox" contains a subdirectory whose name ends with ".default-release", which in turn has a subdirectory "storage/default", which still in turn has a subdirectory whose name starts with "moz-extension+++" followed by hexadecimal digits and hyphens (but not followed by "^userContextId"), which still in turn has a subdirectory "idb", which finally contains the file whose name ends with ".sqlite". The following is a diagram to describe the path. Directories are separated by / as common on Unix-like systems unlike Windows. A sequence of three asterisks (***) indicates an omission of enigmatic string. ~/.mozilla/firefox/ ***.default-release/ storage/default/ moz-extension+++***/ not followed by ^userContextId idb/ ***.sqlite Firefox seems to constrain the maximum size of this ".sqlite" file to 10% of the free space of the partition containing the home directory of the user. I replaced the "idb" directory with a symlink named "idb" which points at a directory (which is also named "idb") on an external USB drive. That is, I deleted the "idb" directory from the partition containing the "~/.mozilla/firefox" directory, and created a symlink named "idb" in the place of the old "idb" directory. Then, I successfully let Firefox write data into the new ".sqlite" file on the external USB drive. However, Firefox continues to constrain the maximum size of this ".sqlite" file to 10% of the free space of the partition containing the home directory of the user. Even after the diversion by symlink, the basis of the constraint is still the partition containing the home directory of the user (instead of the external USB drive), of which 10% is the max size of the new ".sqlite" file residing on the external USB drive. I like neither the 10% constraint itself nor the basis of constraint being the partition containing the home directory of the user. How can the 10% constraint be disabled? I would like the only limitation for the size of the ".sqlite" file to be the free space of the external USB drive. By the way, for those who want to know why I care about this ".sqlite" file, I will explain as follows. There is a certain download manager which is an addon or extension of Firefox. In its multithread mode, this download manager divides the desired file into several parts, and downloads all the parts simultaneously. In certain circumstances, the multithread mode is several times faster than the single-thread mode. This download manager downloads all the parts of a file into the ".sqlite" file first, and then assembles them into a final big file in the Downloads folder or whichever directory that the user specifies. In my use case, 10% of the free space of the partition containing my home directory is too small to receive big files. I wish this download manager could download the multi-parts into an external USB drive in a manner that Firefox does not impose any constraint. However, this download manager cannot let the user specify where the multi-parts should be downloaded to. It downloads the multi-parts into only the ".sqlite" file and nowhere else; and Firefox imposes the 10% constraint on the ".sqlite" file. The user can specify the destination of only the final file assembled from the multi-parts. Anyway, I need to disable the 10% constraint. But how? Thank you in advance.