Pale Moon support is over here: http://forum.palemoon.org/

Pushed the wrong "helpful" button. SInce it has been reported in Firefox before, it obviously isn't a branch-specific issue.

Any clue? Does Firefox have an intentional tag purging?

Are you using Firefox Sync?

Problems with bookmarks and history not working properly can be caused by a corrupted places.sqlite database file.

You can check for problems with the places.sqlite database file in the Firefox profile folder.

• http://kb.mozillazine.org/Bookmarks_history_and_toolbar_buttons_not_working_-_Firefox
• https://support.mozilla.org/kb/Bookmarks+not+saved#w_fix-the-bookmarks-file

• Places Maintenance: https://addons.mozilla.org/firefox/addon/places-maintenance/

There is software like Advanced SystemCare with its Surfing Protection feature that can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.

I'm not using sync, as it has been reported to have problems.

Places seem to work, other than older tags slowly disappearing.

I ran the Places Maintenance plugin once, it did not seem to make any difference.

I am not using any real-time system monitor, other than some default Win7 features.

Is it possible that the tags have a 90-day lifespan or something similar, like history? Or is there a fixed limit on the number of tags?

It is clear that tags are treated differently/separately from bookmarks, and in a poorly designed manner. This causes full tag loss in Sync, backup (now fixed?) and restore. I understand there is something wrong with the "schema" whatever that is. If tags don't have a lifespan limit or number limit, it is possible that hiccups in "schema" department cause some slow partial tag loss.

It does seem to me that the disappeared tags are those that I created awhile ago. I haven't noticed loss of freshly introduced ones tags, this doesn't mean that it doesn't happen but it is likely that the only ones disappearing are the older ones.