Bug 1079725 - Add a BaseInContentPage class. r=aeftimie, r=amatei, r=hskupin

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branch : mozilla-beta
extra : transplant_source : %D1%96%F4a%16%E1%1C%D4%AA2K%219%05%EA%D6%0D%F3%FBk
Bug 987612 - Backed out changeset 3743ab4c2df3. Pushed the wrong commit.

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branch : mozilla-beta
rename : firefox/tests/functional/testAddons/testInstallUninstallHardBlocklistedExtension.js => firefox/tests/functional/restartTests/testAddons_installUninstallHardBlocklistedExtension/test1.js
rename : firefox/tests/functional/testAddons/testInstallUninstallSoftBlocklistedExtension.js => firefox/tests/functional/restartTests/testAddons_installUninstallSoftBlocklistedExtension/test1.js